Legal Bases for Forcible Maritime Interdiction Operations against Terrorist Threat on the High Seas

Eric Louis Corthay


The high seas are sometimes used as a domain from which, through which or within which terrorists conduct activities in preparation of terrorist attacks. These activities comprise, inter alia, the transport of terrorists, materials and weapons, including weapons of mass destruction. Representing a threat to peace and security, these activities are sometimes dealt with by the members of the international community through the carrying out of maritime interdiction operations. The first part of the present paper focuses on the definition, modus operandi, and nature of maritime interdiction operations. Although maritime interdiction operations on the high seas might involve the use of force, the paper argues that they are law enforcement operations that fall outside the scope of the principle prohibiting the use of force which is enshrined in Article 2(4) of the UN Charter.

Maritime interdiction operations, implemented on the high seas in time of peace, are limited by 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. However, the exclusivity rule is not an absolute one from which no derogation is permitted. The second part of the paper aims therefore at clarifying the legal framework in which States can interdict, forcibly if necessary, foreign flagged vessels suspected of conducting terrorist activities. Five legal grounds that allow States to interdict foreign flagged vessels involved in terrorist activities have been identified.

One of the exceptions to the principle of exclusivity is the right of visit detailed in Article 110 of UNCLOS. Even though Article 110(1) can only be invoked in limited circumstances which actually do not explicitly cover maritime terrorism, the paper argues that the provision may nevertheless in some way lead a warship to interfere against a foreign ship that represents a terrorist threat, as demonstrated by the interdiction of the MV So San by a CTF 150 warship (1). In addition, Article 110(1) refers to international treaties that permit maritime interdiction. The paper intends to describe the express and/or implied consent regimes established by international, regional and bilateral treaties signed in response to concerns regarding terrorism and/or the proliferation of WMD and related materials (2). Moreover, consent to interdict may be granted on an ad hoc basis. Here, the paper outlines the criteria that consent must fulfill to be valid and discusses the legality of compliant boarding operations such as those conducted in the context of Operation Active Endeavour (3). Furthermore, the merits of another circumstance precluding wrongfulness, namely state of necessity, as a justification to interdict vessels involved in terrorist activities are discussed (4). Finally, the conditions for the UN Security Council to authorize interference against vessels engaged in terrorist activities are analyzed (5).


Maritime terrorism; Maritime interdiction operations; Right of visit; Consent; State of necessity; UN SC Res 2292

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