At Peace, Yet Under Fire – Blockade Enforcement against Third State Vessels and the U.N Charter

From April 13 to June 18, the U.S.A implemented a blockade against Iran. As part of the blockade enforcement, on June 9th, it attacked the Palau-flagged oil tanker M/T Settebello 20 miles north-east of Sohar in Oman’s Exclusive Economic Zone, resulting in the deaths of three Indian sailors onboard – the first direct deaths caused as part of the U.S blockade enforcement measures. The legal significance of the incident extends far beyond the narrow question of the legality of the attack under the Law of Naval Warfare (LNW). 

The incident illuminates a fault line that runs through the very architecture of public international law itself, one that has never been satisfactorily addressed by international law. How are traditional belligerent rights under the LNW to be reconciled with the U.N. Charter and the rights of states not party to the conflict? This post argues that since the underlying relationship between a belligerent and a neutral State remains one of peace, the LNW cannot by itself supply a lawful basis for the use of force where the U.N. Charter supplies none.

U.S Blockade Enforcement

From April 13 to June 18, the U.S.A implemented a blockade of all maritime traffic entering and exiting Iranian ports. Pursuant to the blockade enforcement, CENTCOM redirected 142 commercial ships, granted passage to 42 ships providing humanitarian aid and disabled 9 vessels, predominantly by way of attacks by U.S naval aircraft. There have also been boardings of vessels like the M/V Blue Star III and M/T Celestial Sea. However, since these vessels were released or diverted, this category of incidents is not explored herein. 

The first six ships attacked were the Iranian flagged M/T Touska (April 19th), M/T Hasna (May 6th) and M/T Sea Star III and M/T Sevda (May 8th), the Gambian flagged M/V Lian Star (May 30th) and the Botswana flagged M/T Lexie (June 2nd). The final three: the Palau flagged M/T Marivex and M/T Settebello and the Guinea-Bissau flagged M/T Jalveer were attacked by U.S. aircraft between June 8 and 10. Palau later stated that the Marivex had already been removed from its registry.

Omani authorities rescued 24 Indian crew members from the Marivex and 21 from the Jalveer. Three of the Settebello’s 24 Indian crew members were killed and the remainder rescued. While foreign flagged, all three vessels had substantial Indian connections extending beyond their crews, potentially including ownership or management, with two also serving Indian ports. Subsequently, India lodged two protests against the attacks by U.S naval forces on commercial vessels carrying Indian mariners, while External Affairs Minister S. Jaishankar relayed India’s deep concern about the use of lethal and deadly force against civilian, commercial shipping to the U.S Secretary of State Marco Rubio, as did the Indian Prime Minister Narendra Modi with the U.S president Donald Trump at the G7 summit. The IMO Secretary General, who had already emphasized that civilian seafarers are not combatants and must never be targeted, expressly condemned the attack on the M/T Settebello.

Attacks on Ships as a use of force

Prior to considering the relationship of the Law of Naval Warfare with the U.N Charter itself, three preliminary issues arise, moving from the relatively settled to the highly contested. First, do attacks against ships constitute a use of force against a State? Second, when do they cross the threshold of an armed attack permitting self-defence? Third, amidst flags of convenience, multinational crews, and opaque ownership structures, who constitutes the victim state?

On the first issue, it is well understood that “forcible conduct that produces harmful effects…in spheres under (a state’s) jurisdiction is prima facie considered to be directed against that (territorial) State.” Consequently, forcible conduct (not grounded in peacetime law enforcement authority) which harms a ship is also understood as being capable of breaching the Article 2(4) prohibition on the use of force (p. 331). However, issues number two and three are characterized by the existence of a legitimate disagreement (p.338). 

On issue two, Article 3(d) of UNGA Resolution 3314 (XXIX) recognizes that an attack on the “marine fleets of another State” may constitute aggression. There is considerable disagreement over the threshold connoted by the term ‘fleets’ (see the references to Ishii, Ruys and Dinstein cited herein). This debate matters because the determination of whether the use of force against shipping constitutes the ‘most grave form of the use of force’ (thus constituting an armed attack) or merely other less grave forms is the very hinge upon which the availability or non-availability of the right to self-defence pivots. 

In the Oil Platforms Case, where the I.C.J addressed this issue in significant detail, it did not find the attack on the Sea Isle City, either by itself or in combination with the other series of attacks to constitute an attack which gave rise to the gravest form of the use of force that would make available the right to self-defence. However, while it arrived at this conclusion in that particular case, the I.C.J did imply (pp.208-209) that it was possible for deliberate and unlawful attacks against merchant vessels to constitute an armed attack. 

The I.C.J’s findings (para 64) in Oil Platforms were heavily informed by the particular facts of the case wherein it had not been possible to determine that the missile fired at the Sea Isle City was aimed at the specific vessel; the fact that the Texaco Caribbean (whatever its ownership was not flying a U.S flag; that there was insufficient evidence to demonstrate that the firing on U.S helicopters and minelaying were done by Iran; and the absence of evidence that the mine which struck the Bridgeton was laid with the specific intention of harming it or other U.S vessels. Notably, none of these incidents resulted in the death of any U.S. national.

The balance (pp.205-206) of views then, leans in favour of rejecting the limitation of Article 3(d) to massive attacks upon a State’s entire merchant fleet. This view most recently found support in U.N.S.C Resolution 2722 (2024) and Resolution 2817 (2026) as well, which recognized the right of states to “defend their vessels from attacks and provocations, including those that undermine navigational rights and freedoms”. 

The confusion on the third issue arises from the divergence between the peacetime and wartime framework, for determining the permissibility of piercing a ship’s veil of registration and considering its ownership, charter or other criteria to ascertain its enemy status and/or ‘genuine link’ with the state whose flag it flies. Whereas the LNW permits this piercing, the International Tribunal on the Law of the Sea (ITLOS) has time (para 83) and again (para 110) prioritized the formal and private functions of the conferral of nationality and registration, while giving insufficient weight to its external public-law functions, particularly its role in determining naval protection or the characterization of vessels during wartime.

Arguably, the international response to the 2022 Russian invasion of Ukraine was a turning point, with states signalling an openness to questions concerning the relationship between registration, the existence of a genuine link, and the recognition of a vessel’s nationality by third States. Indeed, this was prominently on display during the Anglo-American response to attacks against foreign-flagged commercial shipping in the Red Sea in 2024 by the Houthis.

For the present discussion, it suffices to note that the Marivex, Settebello and Jalveer were third state vessels that were not shown to have been carrying weapons or military matériel or performing any belligerent acts. Consequently, forcible action against them implicated the rights of both third states and individuals not party to the hostilities. While the latter are beyond the scope of this article, the following subsection focuses on the former.

The relationship of the Law of Naval Warfare (LNW) and the UN Charter

The U.S use of force against the Marivex, Settebello and Jalveer – attacks that resulted in 3 Indian deaths, has focused the spotlight on the question of what, if any, is the legal basis for using force against third state vessels during blockade enforcement?

A blockade seeks to deny access to an enemy’s coast. Its very effectiveness flows from its property of denying this access to any and all vessels: enemy, non-belligerent and neutral vessels. The legal puzzle is as follows. First, Hague Conventions V and XIII of 1907 recognized that neutral States could maintain their commercial ties with belligerents. Second, since the entry into force of the U.N Charter, there can be no lawful resort to the use of force which cannot be justified via the provisions of the U.N Charter. Given that the relationship between a neutral and a belligerent remains one of a state of peace, how can a blockading state use force against a neutral state without being in breach of its charter obligations?

This problem exposes a fundamental jurisprudential fault line, the answer to which serves as a litmus test (p.3) for how one answers the question posed above (on a spectrum of views, see Kraska for a permissive view and Clapham for a restrictive view). Does Article 2(4)’s prohibition on the use of force constrain belligerent rights under the LNW? Specifically, must the LNW be reconciled with the Charter’s conception of self-defence, or does it apply in its complete pre-Charter form once an armed conflict breaks out?

The expert restatements of the LNW: the San Remo and the Newport manuals subordinate the LNW to the Charter in principle. However, they insulate its substantive rules from the consequences of that subordination in practice. So, on the one hand, they explicitly repudiate (pp.76-77) the notion that the jus ad bellum stops where the jus in bello begins. However, at the same time, they continue to recognize the violability of private property at sea, recognize a practically unlimited conception of military objectives and endorse an understanding of self-defence which is completely at odds with its authoritative and mainstream conception. This informs the viewpoint that there is little evidence that these manuals actually questioned whether the traditional law was actually compatible with the U.N Charter (see Sassòli, p. 433). 

This insulation has gone almost entirely ignored within the mainstream public international law circles, as the absence (pp.426-427) of any general naval war since 1945 – a period when interstate warfighting has predominantly occurred on land and in the air, has resulted in no pressing need to reconcile this tension. As noted by Ingber, the tendency to put a disclaimer upfront about the need to adhere to the Charter, followed by disclaimers and rules which permit Charter inconsistent acts, results in the Charter doing little actual interpretive work. 

However, this lack of clarification has now come to a head. The San Remo and Newport manuals on the law of naval warfare imply – explicitly or by omission – that a blockading state can continue to use force against neutral vessels (and by extension a neutral state if enough of its vessels are targeted), because elements of the LNW that predate (p.473) the U.N Charter endorse precisely such an expansive, pre-Charter conception of violence. The trouble, of course, is that interference with neutral shipping is no longer understood as being legal by default in the post-Charter world – a world that is characterized by a strict regulation of the circumstances in which states may resort to the use of force in their international relations.

Targeting third state vessels pursuant to a blockade, engaging in contraband control and engaging in visit, search diversion and capture are amongst the most permissive and sweeping belligerent privileges that states have sought to claim under the LNW. LNW manuals recognize that these are not automatically available in just any armed conflict. Rather they are conditioned on the scale and duration (p.74) of the conflict, the intensity and scale (pp. 7 and 74) of the armed attack and the gravity of the threat posed. These descriptors function as an ever present, if latent, spectre of the comprehensive (p.83) use of force, rising to the level that triggers the legal regime of ‘war’ as understood in the pre-U.N Charter sense.

Conceptualizing the legal basis for this exact move then necessitates recognizing that these manuals assume two distinct legal orders: one governed by the Charter when force remains below a certain threshold, and another governed by pre-Charter belligerent rights once that threshold is crossed. However, this brings us full circle to the legal problem posed in the preceding paragraphs. How does the fact that an armed conflict acquires an enhanced degree of intensity and scale make any difference whatsoever to the fact that the relationship between a neutral and a belligerent remains one of peace?

Indeed, this tension has also been at play in the U.S publication of contraband lists and an assertion of the ‘right’ to engage in global economic warfare. Notwithstanding the very confused and inconsistent invocation of the different legal bases for its subsequent seizures, what is particularly notable is that despite 12 weeks having elapsed since their publication, the U.S.A has not actually seized a single vessel specifically under this authority.

This reflects the fact that forcible interference with a neutral state’s shipping would fall afoul of the prohibition on the use of force found in Article 2(4) of the U.N Charter. Indeed, the formation of such a consensus which has been remarked (p.135) upon since as early as the 1990s has only grown stronger (pp.331-334) with the passage of time. This has been confirmed in the U.S-Israel and Iran war as well where the U.N.S.C noted in Resolution 2817, the “right of navigation for shipping en route to and from all ports and installations of the littoral States that are not parties to the hostilities.” 

Notwithstanding the explicit recognition of the ongoing conflict as a ‘war’, both the Charter framework and neutrality law do continue (p.272) to discharge a role. The co-existence of a Charter-governed order and the law of neutrality reflects the fact that a neutral and belligerent state continue to be governed by the law of peace – this being the very basis for a neutral state’s entitlement to not be adversely affected by a conflict.

Conclusion

The U.S blockade enforcement has focused attention on a proposition that the LNW assumes but international lawyers rarely confront openly: do there exist circumstances where a state may lawfully use force against another state with which it remains at peace? Irrespective of the view that one adopts about the continuing role discharged by the legal state of war in governing inter-belligerent relations, this article has argued that the LNW cannot, by itself, supply an entitlement to use force against third state shipping where the Charter supplies none. To conclude otherwise is to posit the existence of two legal orders – one governed by the Charter and the other independent of it.