Terrorist Threat on the High Seas Analysis of Some Aspects of the Right of Visit and Self-defence

Vessels of all sizes can be used in a number of ways by terrorists, they can utilize a vessel as a means, a weapon, a bomb, or as a disruption tool. When a terrorist attack happens, it is already too late, hence the critical importance for the International community to take timely, accurate and efficientex ante factosteps.Counter-terrorism measures implemented on the high seas to prevent maritime terrorist attacks from occurring are possible but limited by the International law and notably the law of the sea. To some extent, the law of the sea limits counter-terrorism efforts. On the high seas, enforcement measures against terrorists or terrorist-related activities on board foreign vessels are restricted by the principle of exclusivity of flag State jurisdiction (a). Nevertheless, the application of the principle can be derogated from by the right of visit which provides for, under certain conditions, some leeway to States in their fight against maritime terrorism (b). it is difficult to justify interdiction operations carried out in order to counter terrorist threats on the high seas by the right of self-defence. The first reason relates to the differences in rationale and legal regime between the force deployed during interdiction operations and the one used in self-defence (a); the second reason concerns the existence or not of a right of anticipatory self-defence (b).


I. INTRODUCTION
Covering most of the world's surface, the oceans are a place for many commercial, recreational and military activities 1 . At the same time, the maritime domain, and notably the high seas, is vulnerable to terrorist activities. The hijacking of the Italian Achille Lauro in 1985, the suicide attack in 2000 against the US Navy destroyer Cole, the at- For argument sake, as to date no internationally recognized definition of the term has been adopted, the present writer proposes to define terrorism as being a modus operandi consisting in an unlawful act of intentional violence which induces extreme fear among victims in order to compel a well identified target to do or to abstain from doing any act 4 . Vessels of all sizes can be used in a number of ways by terrorists. Indeed, to further their aims, terrorists can utilize a vessel as a means, a weapon, a bomb, or as a disruption tool 5 . Using this classification, a range of maritime terrorism activities can be postulated, such as using commercial cargo containers to transport terrorists and smuggle materials and weapons, including weapons of mass destruction (WMD), for an unconventional attack on land (vessel as a means); ramming a highspeed boat into warship, cruise liner, ferry or oil tanker; seizing control of a ship and using it as a collision weapon for destroying offshore platforms, port facilities, bridges or other targets on the waterfront (vessel as a weapon); seizing and exploding ships with volatile cargoes in proximity to a land or offshore target (vessel as a bomb); sinking a large commercial cargo in a critical choke-point, or set ablaze to a chemical tanker in a busy strait or port to block traffic or cause pollution (vessel as a disruption tool) 6 . The high seas might therefore be used as a domain from which, through which, or within which maritime terrorist attacks and activities are perpetrated. Even though they do not represent per se a terrorist attack, terrorist activities in preparation of a terrorist attack already represent a terrorist threat that needs to be dealt with by the international community.
When a terrorist attack happens, it is already too late, hence the critical importance for the international community to take timely, accurate and efficientex ante factosteps.Counter-terrorism measures implemented on the high seas to prevent maritime terrorist attacks from occurring are possible but limited by the international law and notably the law of the sea. Indeed, vessels on the high seas are subject to the exclusive jurisdiction and authority of the State whose flag they lawfully fly. In other words, and prima facie, a State A's warship cannot take measures against State B's vessels sailing on the high seas. However, the exclusivity rule is not an absolute one from which no derogation is permitted. International law permits interference with non-national vessels in certain specific circumstances defined by customary or conventional law. One of the derogations or exceptions to the principle of exclusivity is the right of visit (droit de visit)enshrined in Article 110 of the 1982 UN Convention on the Law of the Sea 7 [hereinafter "the 1982 Convention"]. The right of visit authorizes warships on the high seas to conduct maritime interdiction operations against foreign vessels-i.e. visiting, boarding, searching and seizing vessels. From a terminological viewpoint, it must be stressed that the expression maritime 'interdiction' operation is also sometimes called maritime 'interception' operation. The definitions of the two terms -which are not present in the 1982 Convention -are not clear. Authors and States confer to them different definitions, use them sometimes interchangeably 8 and in order to refer to diverse situations (e.g. for the purpose of peacekeeping, to stop boat-people, to suppress threats, or to enforce UN sanctions) 9 . However, as observed by Papastavridis in general the term 'interception' seems to have a broader meaning that the term 'interdiction', in the sense that the former one is a "generic and commonly used term" that "encompass[es] all cases of interference with foreign vessels on the high seas and not only these excused under article 110 of LOSC [Law of the Sea Convention]" 10 .
To some extent, the law of the sea limits counter-terrorism efforts. Pursuant to Article 110 of the 1982 Convention, the right of visit can only be invoked in limited circumstances which actually do not explicitly cover maritime terrorism. States have therefore moved towards the adoptionof treaties that provide for a right of visit in case of maritime terrorism-related threats. These treaties establish express and/or implied consent regimes, but also impose a series of constraints that weaken and slow down counter-terrorism efforts. After analysing the content and scope of application of the principle of exclusivity of flag State jurisdiction, the present paper aims at clarifying some aspects of the right of visit as set forth in the 1982 Convention and other treaties (I). Some States and authors have also justified the lawfulness of interdiction operations carried out to counter terrorist threats on the high seas by the right of self-defence enshrined in Article 51 of the UN Charter. At first sight, this legal path could be seen as an appropriate means to 8 See, e.g. Patricia Mallia, Migrant Smuggling by Sea: Combating a Current Threat to Maritime Security through the Creation of a Cooperative Framework, Leiden, Martinus Nijhoff, 2010, at 21: "the process of "interception" (or interdiction), the ordinary meaning of which is to prevent something from proceeding or arriving, is not limited solely to the migrant smuggling context, but is a tool used in the suppression of other threats". 9 For different definitions from authors or from States, see Efthymios Papastavridis, The Interception of Vessels on the High Seas: Contemporary Challenges to the Legal Order of the Oceans, Studies in International Law, Oxford and Portland, Hart Publishing, 2014, at 60-61. 10 Id., at 61-62. Examples of interference other than those excused under art. 110 of the 1982 Convention are, notably, interference justified by circumstances precluding wrongfulness like consent, state of necessity, or countermeasures. circumvent the problem of the strict application of the right of visit and the constraints created by treaties authorising boarding under specific conditions. Nonetheless, the invocation of the right of self-defence to justify interdiction operations in anticipation of a terrorist attack is still highly dubious. This paper explains that such a perplexity is due to at least two main reasons which relate, firstly, to the different rationales (telos) behind -and therefore the legal regimes governing -the force deployed during interdiction and self-defence operations, and, then, to the question of the existence or not of a right of anticipatory selfdefence (II).

II. THE PRINCIPLE OF EXCLUSIVITY OF FLAG STATE JURIS-DICTION AND THE RIGHT OF VISIT
On the high seas, enforcement measures against terrorists or terrorist-related activities on board foreign vessels are restricted by the principle of exclusivity of flag State jurisdiction (a). Nevertheless, the application of the principle can be derogated from by the right of visit which provides for, under certain conditions, some leeway to States in their fight against maritime terrorism (b).

A. THE EXCLUSIVITY RULE
As a general rule, vessels on the high seas 11 are subject to the exclusive jurisdiction of the State whose flag they lawfully fly. In other words, pursuant to theprinciple of exclusivity of flag State jurisdiction, on the high seas States may not interferewith and have no authority on the vessels of other States.This pillar of the international law of the sea has been invoked by the Permanent Court of International Justice in the Lotus case in these terms: vessels on the high seas are subject to no authority except that of the State whose flag they fly. In virtue of the principle of the freedom of the seas, that is to say, the absence of any territorial sovereignty upon the high seas, no State may exercise any kind of jurisdiction over foreign vessels upon them. 12 156 Volume 14 Number 2 January 2017 Jurnal Hukum Internasional As Reuland observed, "the principle of exclusivity of flag-state jurisdiction[…] is firmly rooted in the axioms of state equality and the freedom of the high seas." 13 Indeed, in Le Louis case, for example, Lord Stowell clearly stated that: [A]ll nations being equal, all have an equal right to the uninterrupted use of the unappropriated parts of the ocean for their navigation. In places where no local authority exists, where the subjects of all states meet upon a footing of entire equality and independence, no one state, or any of its subjects, has a right to assume or exercise authority over the subjects of another. 14 The principle of exclusivity of flag State jurisdiction is codified in international treaties and notably in Article 92(1) of the 1982 Convention, which provides that "[s]hips shall sail under the flag of one State only and, save inexceptional cases expressly provided for in international treaties or in thisConvention, shall be subject to its exclusive jurisdiction on the high seas." 15 The exclusivity rule applies to ships with one nationality.According to Article 91(1) of the 1982 Convention, "[s] hips have the nationality of the State whose flag they are entitled to fly". Article 92(2) of the same Convention states also that "[a] ship which sails under the flags of two or more States […] may be assimilated to a ship without nationality."These ships are assimilated to stateless ships -i.e. ships not sailing under the flag of any State -and as such are not protected under international law 16 .
(1927), at 25. 13  1. An Exception To The Exclusivity Rule: The Right Of Visit The exclusivity of flag State jurisdiction on the high seas in time of peace is not an absolute rule. Article 92(1) of the 1982 Convention points out that ships are subject to the exclusive jurisdiction of the flag State "save inexceptional cases expressly provided for in international treaties or in this Convention". It is worth mentioning that exceptions to the exclusivity rule are not only conventional but might also be customary, as customary rules are sometimes codified in treaties and treaty provisions receive sometimes a customary character throughout time 17

Circumstances Authorising Interference
Article 110 (1) lists a very limitative series of circumstances under which, in time of peace, warships are competent to visit private vessels 23 flying the flag of another State. This is the case when the ship is suspected of being engaged in any one of the activities listed in sub-paragraphs (a) to (c) or of having a doubtful status as per sub-paragraphs (d) and (e). The right of visit has been limited to specific circumstances mainly because States wanted to jealously safeguard as much as possible their exclusive jurisdiction over their own shipping, as well as their rights of property, equality and independence on the high seas 24 .
As terrorism is not expressly listed in paragraph (1), it seems, prima facie and unless a treaty relationship authorises interference, that warships are not authorized to exercise their right of visit against a ship flying the flag of another State when they merely suspect it of being engaged in activities that represent a terrorist threat (e.g. the ship is transporting weapons or people to further terrorist aims). A possible explanation why terrorist threats and, more generally, acts hostile to the State of the warship, have not been included expressis verbis in the scope of Article 110(1) could be drawn from the commentary to the original draft of the 1958 Convention on the High Seas. In its report, the International Law Commission -organ responsible for the draft of the 1958 Convention -observed: The question arose whether the right to board a vessel should be recog-23 According to arts. 95 and 96 of the 1982 Convention, public ships (i.e. a warship or a ship used only on government noncommercial service) "have complete immunity from the jurisdiction of any State other than the flag State". 24 Reuland, supra note 13, at 1167. Seconda facie, however, it seems that Article 110(1) of the 1982 Convention could indirectly lead a warship to interfere against a foreign ship that represents a terrorist threat. This could happen when, once visiting the ship suspected of being engaged in one of the activities listed in sub-paragraphs (a) to (c) or of having a suspicious status as per subparagraphs (d) and (e), evidence of proscribed terrorist activities is discovered (e.g. explosive devices ready to be activated, map with location of targets). Here, the interference is contingent upon the existence, first, of a reasonable suspicion that the foreign ship has an uncertain status or is engaged in one of the activities listed in paragraph (1). For example, crews of an interfering warship visit a ship that "sails under the flags of two or more States, using them according to convenience" 26 , or a ship that is "not flying a national flag or bearing equivalent markings identifying its nationality" 27 , and, when searching on board the interfered ship, some forms of preparation for a terrorist attack are detected. Thisoccurred on December 9, 2002, on the high seas, off the coast of Yemen, when two Spanish Navy vessels intercepted and boarded the So San, a North Korean cargo ship. The Spanish Navy justified the boarding on grounds that the ship was not flying a flag and its national markings were obscured by paint 28 . When searching, the boarding crews found Scud missiles hidden beneath cargo. At the time of the discovery, it was not known whether the Scud missiles had been legally purchased by Yemen, or whether they were going to be delivered to terrorist organizations 29 . A similar scenario is when the warship's crews are ascertaining the status of a ship that, "though flying a foreign flag or refusing to show its flag, […] is, in reality, of the same nationality as the warship" 30 , and then, once on board, they notice that the ship is engaged in terrorist activities. Acting this way, the ship certainly tries to hide its identity. Indeed, for the international Law Commission, when a ship conceals its nationality which is in reality the same nationality of the warship "it is permissible to presume that the ship has committed unlawful acts, and the warship should be at liberty to verify whether its suspicions are justified" 31 . Should suspicions of any engagement in terrorist activities be confirmed, it would be very surprising that the boarding warship be not allowed to bring the boarded vessel to account.
Article 110(1) of the 1982 Convention also refers to 'acts of interference [that] derive from powers conferred by treaty'. It means that international treaties permit the right of visit in circumstances other than those specified in sub-paragraphs (a) to (e).Several international treaties have been signed in response to concerns regarding terrorism and/or the proliferation of WMD and related materials. Such treaties represent "an important advance in devising a lawful means for the exercise of the right of visit against a foreign flagged vessel on the high seas" 32 . Indeed, all these treaties establish express and/or implied consent regimes. Nevertheless, they also provide for some provisions that could significantlyslow down the exercise of the right of visit. targeting of a ship in a terrorist attack 34 . When a State Party suspects a ship of being involved in the commission of an offence set forth in the Protocol, it shall request that the flag State confirm the claim of nationality 35 . As per Article 8bis(2), each request shall respect certain constraints, like containing the name of the suspect ship, the IMO ship identification number, etc. Also, if a request is initially made orally, it must be confirmed in writing as soon as possible. Then, pursuant to Article 8bis(5)(b), express consent for boarding and searching must be granted by the flag State: If nationality is confirmed, the requesting Party shall ask the first Party (hereinafter referred to as "the flag State") for authorization to board and to take appropriate measures with regard to that ship which may include stopping, boarding, and searching the ship, its cargo, and persons on board, and questioning the persons on board in order to determine if an offense set forth in article 3, 3bis, 3ter or 3quarter has been, is being or is about to be committed.
It is important to mention that, in that case, the flag State may either decide to conduct the boarding and search itself,permit the other State to do so, or decide that both States may do so together, or the flag State has the option of denying permission to board and search 36 .
The 2005 SUA Protocol alsoprovides an implied consent regime. Article 8bis(5)(e) states: Upon or after depositing its instrument of ratification, acceptance, approval or accession, a State Party may notify the Secretary-General that, with respect to ships flying its flag or displaying its mark of registry, the requesting Party is authorized to board and search a ship, its cargo and persons on board, and to question the persons on board in order to determine if an offence set forth in article 3, 3bis, 3ter or 3quater has been, is being or is about to be committed 37 . Cooperation Agreement [hereinafter "CARICOM Agreement"] 38 . As at August 2016 the Agreement is still not yet in force. The objective of the Agreement is to promote cooperation among States Parties to enable them to conduct law enforcement operations that relate to, inter alia, combating terrorism 39 . Like the 2005 SUA Protocol, the CARICOM Agreement sets forth an express and implied consent regime 40 . However, some provisions of the Agreement also negatively affect the efficiency of counter-terrorism efforts. For example, request for verification of nationality of a suspected vessel, before the actual boarding and search, "may be conveyed orally but shall later be confirmed by written communication" which contains specific indications 41 . Then, once the nationality of the vessel is verified, the flag State can still decide whether the boarding and search is conducted by its own forces, or by the requesting Party's forces, or by both countries' forces, or whether it prefers to deny permission to board and search 42 .
At the bilateral level, finally, the United States has signed bilateral boarding agreements with several States (Antigua and Barbuda, Bahamas, Belize, Croatia, Cyprus, Liberia, Marshall Islands, Malta, Mongolia, Panama, St. Vincent and the Grenadines). The Agreements establish authority to board foreign vessels suspected of carrying illicit shipments of WMD and related material 43 ; they establish implied and/or express consent regimes 44 , and some provisions also limit how quickly 38 CARICOM Maritime and Airspace Security Cooperation Agreement (opened for signature Jul. 4, 2008), available at http://archive.caricom.org/jsp/secretariat/legal_instruments/agreement_maritime_airspace_security_cooperation.pdf.

Modus Operandi
With regard to the modus operandi of the right of visit, Article 110(2) of the 1982 Convention states: In the cases provided for in paragraph 1, the warship may proceed to verify the ship's right to fly its flag. To this end, it may send a boat under the command of an officer to the suspected ship. If suspicion remains after the documents have been checked, it may proceed to a further examination on board the ship, which must be carried out with all possible consideration.
According to paragraph (2), the right of visit is composed of two distinct operations: ledroit d'enquête du pavillon (right of investigation of flag) and the right of search 46 . Taken together, these two distinct phases are encompassed within the umbrella term ofmaritime interdictionoperation. The purpose of the first phase of the right of visit -ledroit d'enquête du pavillon -is to "verify the ship's right to fly its flag", i.e. to verify the true nationality of a vessel the warship encounters.In concreto, the warship verifies the papers of the ship, i.e. the documents issued by the flag State which granted to the ship the right to fly its flag 47 . The warship is authorized to exercise its right of investigation of flag only in the cases in which the ship is reasonably suspected of being engaged in some proscribed activity. The criterion of 'reasonable ground' for suspicion 48 is difficult to define in abstracto.It has to be assessed on a case by case basis. Authors converge, however, on the view that an appropriate reasonable ground standard lies somewhere between mere suspicion and actual knowledge of an infringement 49 .Nowadays, modern technologies facilitating surveillance, reconnaissance,intelligencegathering and information-sharing, help establish the existence of a reaons of Mass Destruction, Their Delivery Systems, and Related Materials By Sea. 45  In order to ascertain whether or not the ship carries the proper papers on board, the ship must stop its journey. In case of absence of compliant or consensual boarding by the master of the vessel 51 , the warship adopts graduated measures in order to stop the ship. Reuland explains the procedure as follows: "[t]o effect a stoppage, the warship will hail the suspect vessel or, if this is impossible or ineffectual, fire across her bow. Should the suspect vessel prove obstinate, the warship may use reasonable force." 52 After the stoppage, comes the actual boarding for However, Reuland, supra note 13, at 1175, footnote 33, expresses some concern with regard to such an option: "With respect, it does not seem prudent to require an officer of the suspect ship to carry the vessel's papers to the warship for two reasons: first, the papers of a vessel should never be exposed to chance of loss; and second, suspicion may remain after the papers are examined and it may be Volume 14 Number 2 January 2017 suspicions are dissipated after examination of the papers, the ship is allowed by the warship to go its way 55 .
If, after the documents have been checked, suspicion remains -or a new suspicion has arisen 56 -that the ship is engaged in some proscribed activity,the warship may proceed to a further examination on board the ship. Here, the warship proceeds to the second phase of the right of visit, i.e. the right of search.This second and more intrusive step aims at discovering evidence that would confirm the suspicions of the warship, and "must be carried out with all possible consideration" 57 .
The search leads to two different situations: either to the confirmation that the ship is engaged in proscribed activities, or to the dissipation of all suspicions. In the former case, "the warship may arrest the vessel or otherwise bring the vessel to account" 58 . Oppenheim explains: Arrest is effected through the commander of the arresting man-of-war appointing one of her officers and a part of her crew to take charge of the arrested vessel. This officer is responsible for the vessel, and for her cargo, which must be kept safe and intact. The arrested vessel, either accompanied by the arresting vessel or not, must be brought to such harbor as is determined by the cause of the arrest 59 .
In the latter case, article 110(3) of the 1982 Convention provides that "[i]f the suspicions prove to be unfounded, and provided that the ship boarded has not committed any act justifying them, it shall be compensated for any loss or damage that may have been sustained." 60 necessary to proceed to the merchantman in order to search her. In all cases, then, a warship exercising her droit de visite should do so aboard the suspect vessel." 55 Openheim, id. 56 Reuland, supra note 13, at 1175, footnote 36. 57 Oppenheim, supra note 54, at para. 269, explains: "Search is effected by an officer and some of the crew of the man-of-war, the master and crew of the vessel to be searched not being obliged to render any assistance whatever, except to open locked cupboards and the like. The search must take place in an orderly way, and no damage must be done to the cargo. If the search proves everything to be in order, the searching party must carefully replace everything removed, a memorandum of the search is to be made in the log-book, and the searched vessel is to be allowed to proceed on her course". 58 Reuland, supra note 13, at 1176. 59 Oppenheim, supra note 54, at para. 270.

B. SELF-DEFENCE TO JUSTIFY MARITIME INTERDICTION OPERATIONS AGAINST TERRORIST THREATS?
As noted above, the right of visit enshrined in Article 110 of the 1982 Convention provides limited leeway to States when they want to interdict a ship that poses a maritime terrorist threat. Indeed, if no 'powers conferred by treaty' exist, the warship's interference must be contingent upon the existence of a reasonable suspicion that the foreign ship is engaged in one of the activities listed in the said Article, otherwise the interdicting operation cannot be carried out. Furthermore, the existence of a treaty authorizing a warship to visit a vessel suspected of being involved in terrorist activities is not always sufficient to enhance maritime security. Flag State delay or denial in authorisation of the visit, or request for obstructive conditions in conducting a boarding, for instance, all could increase the risk of missing the opportunity to thwart a terrorist attack. A certain number of authors 61 , but few States (see infra), have therefore decided to take another path to tackle maritime terrorist threats. They argue that the right of self-defence is appropriate to justify maritime interception operations (i.e. stopping, boarding, searching, seizing) against vessels engaged in terrorist activities or, more generally, vessels viewed as posing a security threat to them (e.g. vessels carrying nuclear or other sensitive materials and technologies for illicit purposes).
The customary right of self-defence is enshrined in Article 51 of the mentioning however that the incident did not happen on the high sea but in the English Channel. That cargo ship was carrying 26,000 tonnes of raw sugar to the Tate and Lyle sugar refinery in Silvertown, east London, when, suspected of carrying terrorist material, it was interdicted by British authorities. After a five-day search, suspicion proved unfounded and the ship was allowed to complete its journey.

UN Charter. The first sentence provides:
Nothing in the present Charter shall impair the inherent right of individual or collective self-defence if an armed attack occurs against a Member of the United Nations, until the Security Council has taken measures necessary to maintain international peace and security.
This provision subordinates recourse to the right of self-defence "to certain restrictions and to specific rules" 62 . In the opinion of the present writer, an action in self-defence can only be triggered in case of armed attack by a State. The requirement for an armed attack to exist was confirmed in the Nicaragua case by the International Court of Justice [hereinafter "the Court"] which held that such an attack is "the condition sine qua non required for the exercise of the right of […] self-defence" 63 . The answer to the question whether a particular form of use of force by a State might be qualified as an armed attack depends upon the degree of gravity of the said act 64 . With regard to the question whether an armed attack must be attributed to a State or whether it may be carried out by non-State actorswho have no sufficient connection with a State for attributing their violent conduct to that State, the Court has recalled for almost forty years that an armed attack is and must be understood as being an act of State. For example, in the Wall case, when answering the question whether the construction of a wall between Israel and Pal-62 Roberto Ago, 'Addendum to the eighth report on State responsibility: The internationally wrongful act of the State, source of international responsibility', Y.B. Int'l L. Comm'n, Vol. II, Part. One, 1980, at 63, para. 108 104-117. In Nicaragua case, the Court held: "As regards certain particular aspects of the principle [prohibiting the use of force], it will be necessary to distinguish the most grave forms of the use of force (those constituting an armed attack) from other less grave forms." Nicaragua case, id., para. 191. Referring to the Friendly Relations Declaration, the Court stated also that "organizing, instigating, assisting or participating in […] terrorist acts in another State or acquiescing in organized activities within its territory directed towards the commission of such acts" are examples of what constitute "less grave forms" of use of force and not armed attacks. Id.

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Volume 14 Number 2 January 2017 Jurnal Hukum Internasional estine could be justified by the right of self-defence, the Court held that "Article 51 of the Charter […] recognizes the existence of an inherent right of self-defence in the case of armed attack by one State against another State." 65 Then, as "Israel [did] not claim that the attacks against it are imputable to a foreign State" the Court concluded that Article 51 of the UN Charter had no relevance in this case 66 .Last but not least, the action taken in self-defence must comply with the customary 67 requirements of the necessity, proportionality and immediacy (see infra).
It is well known that, since the adoption of the UN Charter in 1945, almost every single point related to the conditions of invocation and the conditions of implementation of the right of self-defence are debated by the scholars and show divisions between States 68 . This paper does not intend to address all the issues surrounding this right but focuses on two reasons why it is difficult to justify interdiction operations carried out in order to counter terrorist threats on the high seas by the right of self-defence. The first reason relates to the differences in rationale and legal regime between the force deployed during interdiction operations and the one used in self-defence (a); the second reason concerns the existence or not of a right of anticipatory self-defence (b).

Two Types of Use of Force
As reflected in the Articles on Responsibility of States for Internationally Wrongful Acts 69 , self-defence is a circumstance precluding wrongfulness 70 . However, it does not exclude the wrongfulness of any kind of conduct, but only the wrongfulness of an act of use of force banned by the international law. Ago observed that "self-defence is to be regarded as an exceptional circumstance precluding the wrongfulness of conduct inconsistent with a general obligation to refrain from the use of force" 71 .
The use of force which States have the obligation to refrain from is the one referred to in Article 2(4) of the UN Charter which codifies the fundamental principle prohibiting the use of force by States in their international relations. Article 2(4) provides:

All Members shall refrain in their international relations from the threat or use of force against the territorial integrity or political independence of any state, or in any other manner inconsistent with the Purposes of the United Nations.
The term 'force' mentioned in Article 2(4) of the UN Charter is limited to the notion of direct or indirect 'armed force' 72 . A clear example of armed force is the military force deployed by the different components of the national defence forces (army, navy, air forces), as it is the case during wars, aggressions, and their counterpart: self-defence operations.
It should be noted, here, that interdiction operations,also,might imply the commitment of national defence forcesand the recourse to armed force. With regard to the United States' practice, Allen writes:  Allen also observes that interdiction (interception) operations might occasionally require the use of force: Even though the use of force that might be carried out during interdiction operations at sea is not generally prohibited 75 ,it is not left at the sole discretion of the intercepting State but must rather respect specific requisites: the use of force must be avoided as far as possible, and, if unavoidable, it must respect the standards of reasonableness and necessity. In the M/V 'Saiga' (No. 2) case, for example, the International Tribunal for the Law of the Sea stated: In the same judgment, the Tribunal concluded that these three principles -unavoidability, reasonableness and necessity 77 -"have been followed over the years in law enforcement operations at sea" and represent "[t]he basic principle[s] concerning the use of force in the arrest of a ship at sea" 78 .
Similarly, military operations conducted in self-defence must also comply with specific requirements. These "essential conditions for the admissibility of the plea of self-defence in a given case" 79 are the three requirements of necessity, proportionality, and immediacy (see infra). The requirement of necessity was described by Ago as follows: "[t]he reason for stressing that action taken in self-defense must be necessary is that the State attacked […] must not, in the particular circumstances, have had any means of halting the attack other than recourse to armed force" 80 .With regard to the condition of proportionality, Ago contended that "[t]he requirement of the proportionality of the action taken in self-defense […] concerns the relationship between that action and its purpose, namely -and this can never be repeated too often -that of halting and repelling the attack" 81 .
Notwithstanding the fact that both interdiction operations and actions in self-defence can be conducted by military personnel and must respect specific requisites, it is important to emphasise that the use of force authorized during interdiction operations, when boarding and searching a private vessel on the high seas in time of peace, is intrinsi- cally distinct from the use of force referred to in Article 2(4) of the UN Charter 82 and carried out during a self-defence operation in reaction to an armed attack. Indeed, the two notions of use of force are conceptually different 83 and governed by two different bodies of rules 84 .The use of force mentioned in Article 2(4) of the UN Charter refers to the conduct of a State directed against another State, and is covered by the relevant provisions of the UN Charter. In contrast, the limited use of force authorized in the course of interdiction operations in time of peace "refer[s] to the means used by authorized government vessels and their agents to compel individuals to comply with enforcement actions" 85 . The force used during interdiction operations relates, therefore, to maritime law enforcement activities (i.e. police measures) against private vessels.This form of use of force is governed by the law of the sea and does not violate Article 301 of the1982 Convention which requires States to refrain from any threat or use of force inconsistent with the UN Charter.Furthermore, these two common usages of the term force have different rationales: while the purpose ofthe interdiction of the use of force under Article 2(4) of the UN Charter -and its exception: the right of self-defence -is the protection of "sovereign rights" (e.g. territorial integrity, political independence), the aim of the police force deployed during interdiction operations is "the advancement of the interests of international community" 86 .

The alleged right of anticipatory self-defence
In a world where oceans can be used by terrorists -or other actors who intend to support terrorists-who threaten members of the international community and have decided, in the not too distant future, to attack them, the question is raised of the legality of an action in selfdefence in anticipation of their attacks.
a. The doctrine of anticipatory self-defence The doctrine of anticipatory self-defence, according to which an action in self-defence could be triggered before an armed attack occurs,has beensupported by some scholars for a long time 87 . Even more support is given since the upsurge of counter-terrorism and counter-proliferation efforts 88 .The concept of anticipatory self-defence has also been referred to in the maritime security context 89 . For example, Bowett states: It can scarcely be contemplated that a state must remain passive whilst a serious menace to its security mounts on the high seas beyond its territorial sea. It is accordingly maintained that it is still permissible for a state to assume a protective jurisdiction, within the limits circumscribing every exercise of the right of self-defence, upon the high seas in order to protect its ships, its aircraft, and its rights of territorial integrity and political independence from an imminent danger or actual attack 90  More specifically, anticipatory self-defence has been invoked as a legal justification for the interdiction of vessels engaged in unlawful activities. For example, Colombos contends: The right of self-defence, as recognized by the law of nations, will confer on a State, in a case where its safety is threatened, a self-protective jurisdiction which will entitle it to visit and arrest a vessel on the high seas and to send her in for adjudication 91 .
From a semantic viewpoint and before analysing the validity in law of the doctrine of anticipatory self-defence, it must be stressed that the terms 'anticipatory self-defence', 'preventive self-defence', 'preemptive self-defence' have no recognized definitions in international law. Sometimes, authors and governments use the same term to express different ideas 92 . For the sake of clarification, in the present paper the term anticipatory self-defence embraces the two concepts of preventive self-defence and pre-emptive self-defence.
Preventive self-defence is invoked when the launch of an attack is imminent. Understanding the meaning of that term is helped by referring to the US doctrine. In the 2007 Operational Law Handbook, the US Government -who called it anticipatory self-defence -defines preventive self-defence as follows: Anticipatory self-defense justifies using force in anticipation of an 'imminent' armed attack. Under this concept, a State is not required to absorb the 'first hit' before it can resort to the use of force in self-defense to repel an imminent attack. 93 The 2007 Operational Law Handbook also contends that the right of preventive self-defence is a customary right "which was not 'negotiated' away under the Charter" 94 .According to the US Government, the roots of preventive self-defence were found in the now famous statement made by Secretary  For the US Government, the implementation of the right of preventive self-defence requests the fulfilment of certain conditions: "the right of anticipatory self-defense has been predicated upon knowing, with a reasonable level of certainty, the time and place of an enemy's forthcoming attack" 96 .
Later on, in the aftermath of the 9/11 terrorist attacks, the Bush Administration explained that the United States "must adapt the concept of imminent threat to the capabilities and objectives of today's adversaries" 97 . Two factors led to the adaptation of the concept of imminence: the devastating destructive nature of weapons of mass destruction that could fall from rogue States into the hands of terrorists (capabilities) 98 , and the very intention of terrorists and rogue States to The important point is that the similarity between both doctrines (preventive and pre-emptive self-defence) lies in the fact that there is, in both cases, a high level of certainty that an attack will occur. The difference, however, concerns the level of certainty as to the time and place of the forthcoming attack 101 .

Rejection of a Right of Anticipatory Self-Defence
Even though the existence of a customary right of anticipatory self-defence is supported by some scholars and States, the analysis of the purpose of the customary law of self-defence as understood at the dawning of the adoption of the UN Charter, the interpretation of the letter and spirit of Article 51 of the said Charter, the actual State practice subsequent to the adoption of it, as well as the view of the International Court of Justice, all lead to the conclusion that to date the alleged right of anticipatory self-defence has no place in international law.
Acting in self-defence to prevent or deter a future attack is nothing more than implementing the nineteenth century concept of self-help (or self-preservation, self-protection). At that time, the two concepts -self-defence, self-help -were very similar; both expressed the right for the State to ensure its own security 102 .In the 1837Caroline case, for instance, the two notions were indistinctly associated 103 . During the nineteenth century, self-defence (or self-help) was invoked in many differing situations. Humphrey Waldock observed that legitimate self-defense has three main requirements: (1) An actual infringement or threat of infringement of the rights of the defending State; (2) A failure or inability on the part of the other State to use its own legal powers to stop or prevent the infringement; and (3) Acts of self-defense strictly confined to the object of stopping or preventing the infringement and reasonably proportionate to what is required for achieving this object 104 . However, during the 1920s' and 1930s' the concept of self-defence has progressively emerged as an exception to the prohibition of the use of force. Simultaneously, the purpose of an action in self-defense has been significantly narrowed. Indeed, Linos-Alexandre Sicilianos, who analysed State practice during the inter-war period, came to the conclusion that self-defence was perceived at that time as only a reaction, a reaction against an attack, an armed attack or an invasion 105 . Therefore, during the 1930s and especially at the time of the adoption of the UN Charter in 1945, the purpose of the right of self-defence had been limited to the one of halting and repelling an actual armed attack.
or collective self-defence if an armed attack occurs" 106 . The wording "if an armed attack occurs" is very restrictive; it does not mean "if the threat of an armed attack occurs". In other words, a textual interpretation of Article 51 leads to the conclusion that the existence of an actual armed attack is an imperative condition for the exercise of the right of self-defence 107 . Kunz,who contended that the right of self-defence "does not exist against any form of aggression which does not constitute 'armed attack', wrote: In addition, purposive interpretation of the UN Charter also supports the argument of a rejection of a right of anticipatory self-defence. Indeed, the will of those who drafted the UN Charter was to limit as much as possible the right for States to use force in their international relations. Their aims were not to recognize a right of self-protection that could be invoked every time a State is threatened 109 . Use of force in case of threat to international peace and security can only be envisaged through the system of collective security. This system is, primarily 110 , in the hands of the Security Councilwhich has the monopoly of the use of force in prevention of acts injurious to international peace and security 111 .
It is therefore apparent that in 1945 the ratione temporisscope of the right of self-defence has received a very restrictive interpretation. The analysis of actual State practice subsequent to the adoption of the UN Charter confirms such a strict interpretation and the lack of evolution of a customary right that would authorize military operations in anticipation of an armed attack.
State's practice related to the invocation of anticipatory self-defence as a ground for the interdiction of vessels is limited to few cases 112 .In January 2002, Israel Defence Forces intercepted the Karin A, an Iraqiflagged ship carrying, according to Israel, weapons for the Palestinian Authority. The Permanent Representative of Israel to the United Nations stated that "their seizure constitutes a vital act of self-defence and an important counter-terrorist measure" 113 . While most of the international community did not comment on the legality of the Israeli operation 114 , the then-US Defence Secretary, Donald Rumsfeld, qualified the Israeli operation as "a legitimate act of self-defense, noting that the US had conducted similar maritime operations" 115 . Indeed, after the 9/11 terrorist attacks, the United States boarded vessels in the Indian Ocean, the Red Sea and the Strait of Hormuz in search of Osama bin Laden and his henchmen 116 . Dyke notes that "[a]lthough the specific legal basis operations notably as aggressions 121 or acts of aggression 122 . Thus, it appearsthat States are divided on the question whether the right of anticipatory self-defence has a place in international law. The actual practice of the international community of States as a whole being not uniform, as well as not constant, a customary right of anticipatory self-defence has not (yet) been able to emerge 123 .
Same conclusions can be drawn from an analysis of the judgment of the International Court of Justice. Even though, in the Nicaragua case of 1986, the Court did not discuss "the lawfulness of a response to the imminent threat of armed attack" because of the circumstance in which the dispute had arisen between the Parties 124 , the wording used by the Court implicitly indicates a rejection of the right of anticipatory self-defence. Thus, in paragraph 176 of the judgment, the Court notes that the Charter "does not contain any specific rule whereby self-defence would warrant only measures which are proportional to the armed attack and necessary to respond to it, a rule well established in customary international law" 125 . In paragraph 195, she declares that "[i]n the case of Volume 14 Number 2 January 2017 Jurnal Hukum Internasional individual self-defence, the exercise of this right is subject to the State concerned having been the victim of an armed attack." 126 And finally, in paragraph 232, the Court held that "[t]he exercise of the right of collective self-defence presupposes that an armed attack has occurred." 127

III.CONCLUSION
The discrete circumstances under which the right of visit enshrined in Article 110 of the 1982 Convention can be invoked do not explicitly include maritime terrorism. However, terrorism is one of the major threats to maritime security. Members of the international community have therefore devised multilateral, regional and bilateral treaties to permit interdictions against ships suspected of being involved with terrorist acts on the high seas. These legal instruments are a significant addition to counter-terrorism efforts. Nevertheless, given the still primordial importance accorded by States to freedom of navigation and the exclusive jurisdiction of the flag State, ship boarding treaties have been drafted with many constraints that hinder their effectiveness (e.g. conditions for a valid request, emphasis on express consent of a flag State for boarding, possibility of obstructive conditions in conducting a boarding).
Given the limited room offered by Article 110 of the 1982 Convention and the weaknesses of the ship boarding treaties, it is understandable that States and authors are suggesting and following other paths to respond to maritime terrorist threats. Not all of them are however legal. The right of anticipatory self-defence, for example, still does not exist under international law, and therefore any maritime interdiction operations carried out to prevent or deter a maritime terrorist attack from occurring cannot be justified by that alleged right. That is not to say that the right of self-defence cannot be invoked by those fighting against terrorism on the high seas, but for that right to be properly invoked the conditions of its invocation and implementation must be fulfilled. In other word, to be lawful under the right of self-defence, the maritime operation must respect the requirements of necessity, proportionality and immediacy, and its aim must be limited to stopping or repelling an actual terrorist attack which is attributed to a State and has a sufficient level of gravity. But given that terrorist attacks are most of the time very swift, opportunities to invoke a right of self-defence are rare.
Successfully preventing and deterring maritime terrorist attacks definitely serve all States. The international community must therefore put all necessary efforts in that regard. One solution would be to give precedence to common interests (i.e. maritime security) over exclusive jurisdiction rules, by for example adopting new ship boarding treaties with fewer constraints. Other avenues to explore further could be to adopt efficient mechanisms to ensure full respect for UN Security Council decisions (e.g. Resolution 1373 (2001) and Resolution 1540 (2004)),to emphasize international cooperation and collaboration in the maritime domain (e.g. efficient intelligence gathering and sharing), and of course to address the root causes of terrorism.