Chaos in the Strait of Hormuz: Rights, Rules and State Responsibility

The Military Conflict

On 28 February 2026, the United States and Israel launched widespread, coordinated missile, unmanned aerial vehicle (drone) and airstrikes against targets in Iran - the stated aim of the operation being to induce regime change and target the Iranian nuclear and ballistic missile programmes. While the Strait of Hormuz remained technically open, maritime traffic was effectively brought to a standstill following suspended transits, halted tanker movement, insurance withdrawal, and precautionary vessel positioning across the Gulf of Oman. The legality and justification for this military action has been the subject of ongoing debate at the diplomatic level and is not further discussed here. It should be noted that while the United States never issued a formal declaration of war or an Authorization for the Use of Military Force against Iran, it nevertheless maintained a military campaign against Iran under Operation Epic Fury for over 50 days prior to publication of this advice.

In retaliation for the airstrikes, Iran launched missile and drone counter attacks on Bahrain, Kuwait, Oman, Qatar, Saudi Arabia and the United Arab Emirates on 28 February 2026. The Iranian Revolutionary Guard Corps ('IGRC') also announced that the Strait of Hormuz was closed. Four commercial tankers were struck in the Strait and in the Gulf of Oman within 36 hours of the commencement of Operation Epic Fury. No public claim of responsibility for individual vessel strikes has been documented and it is entirely unclear whether these were deliberate tanker attacks or collateral to missile, drone, or asymmetrical exchanges in the area of hostilities.

On 2 March 2026, the IGRC announced a unilateral closure of all maritime traffic through the Strait of Hormuz and warned that vessels attempting transit would be targeted. This led to an immediate reduction of transit through the Strait over the period 2 March – 11 March, with recorded commercial vessel crossings far below typical baseline levels, reflecting the enforcement of the closure by Iran and a broader absence of commercial confidence in safe passage through the Strait. A structural insurance shock within the global maritime risk market was also sparked by the onset of hostilities, with several major Protection and Indemnity insurers issuing cancellation notices on Gulf war-risk coverage and reinsurance capacity from London markets temporarily withdrawn.

On 11 March 2026, the situation worsened further following reports of multiple attacks on commercial vessels and of preparations being made by Iran to deploy naval mines in the Strait. The deterioration of the situation prompted the United Nations Security Council to adopt Resolution 2817 (2026), which inter alia, condemned 'in the strongest terms' Iranian military attacks against nations across the Middle East region, and declared the actions of Iran to amount to a breach of international law and to constitute a serious threat to international peace and security. The Resolution also condemned any actions or threats by Iran 'aimed at closing, obstructing, or otherwise interfering with international navigation' through the Strait of Hormuz and declared any attempt to 'impede lawful transit passage or freedom of navigation' in the Strait of Hormuz to constitute a serious threat to international peace and security and called upon Iran to immediately refrain from any such actions or threats.

On 25 March, U.S. Central Command reported that the United States had struck over 10,000 targets in Iran, including missile and drone sites, Iranian naval assets, Iran's military industrial base, and command and control centers associated with the Iranian military and the IRGC. On 27 March, the IGRC announced that the Strait of Hormuz was closed to any vessel going to or from the ports of the United States, Israel and their allies. Access again became less predictable, with multiple vessels denied passage based on ownership and geopolitical alignment. This trend continued until early April 2026.

On 7 April 2026, a draft Security Council Resolution submitted by several Gulf States concerning the coordination of defensive efforts to secure freedom of navigation in the Strait of Hormuz was rejected by the Council.

Following mediation by Pakistan supported by Turkey and Egypt, a two-week ceasefire of hostilities involving the United States and Iran (not officially including Israel) was announced on 8 April 2026. Despite the ceasefire, there was no return to open commercial maritime navigation through the Strait of Hormuz — transit remained restricted, coordinated, and selectively enforced by Iran. On 12 April 2026, ongoing peace talks between the United States and Iran following the ceasefire collapsed.

On 13 April 2026, the United States announced a blockade of all maritime traffic entering or exiting Iranian ports. Although it was at one point publicly stated that the blockade would apply to all maritime traffic entering or seeking to exit the Strait of Hormuz, this was not reflected in the official terms of engagement for the blockade, which was expressly limited to vessels entering and exiting Iranian ports.

On 17 April 2026, the Foreign Minister of Iran released a statement declaring that the Strait of Hormuz was 'completely open' for all commercial vessels for the remaining period of ceasefire, on the coordinated routes previously announced by the Ports and Maritime Organisation of Iran. However, this was quickly rescinded on 18 April 2026, following an announcement that the Strait of Hormuz was again closed, and would remain closed until the United States ended the blockade of Iranian ports.

Following the announcement of 18 April 2026, the IRGC seized the Panama-flagged MSC Francesca (IMO 9401116) and Liberia-flagged Epaminondas (IMO 9153862). Both were linked to MSC, the world's largest container line, which the IRGC said was banned from transit through the Strait of Hormuz due to links between MSC and Israel.

During the period 8 April 2026–30 April 2026, commercial transits and navigation through the Strait of Hormuz was down 93%. Nearly 900 cargo ships and tankers remained trapped in the Persian Gulf.

On 1 May 2026, the President of the United States formally notified Congress that hostilities between the United States and Iran had terminated following the ceasefire announced on 8 April. A further Presidential statement was issued on 3 May 2026 announcing that the United States would as a humanitarian gesture commence guiding ships from neutral countries out of the Strait of Hormuz under 'Project Freedom', which formally began on 4 May 2026.

In response to the announcement of Project Freedom, Iran issued a statement declaring that any transit through the Strait of Hormuz must be coordinated with the armed forces of Iran. A direct warning was also issued to commercial vessels urging them to avoid any transit without prior coordination with Iran and that any failure to do so would jeopardize their safety.

On 5 May 2026, Iran announced the establishment of a new government body called the Persian Gulf Strait Authority ('PGSA') administered by the IRGC to regulate Iranian control over maritime traffic transiting the Strait of Hormuz. Under the new arrangements, commercial vessels seeking to transit the Strait would be required to obtain authorization through an official permit system managed via email.

On 6 May 2026, the President of the United States announced a temporary suspension of Project Freedom, in order to allow talks between the United States and Iran to progress. It was however made clear in the announcement that the blockade of Iranian ports would remain in effect.

During the period 28 February – 15 May 2026, there were 49 reports of incidents affecting vessels operating in and around the Strait of Hormuz and Gulf of Oman, with 27 reports of attacks on vessels, 20 reports of suspicious activity and 2 hijack reports.

Geography and Legal Status

The Strait of Hormuz is a deep, narrow channel approximately 21 nautical miles (‘nm’) wide at its narrowest point that connects the Persian Gulf to the Gulf of Oman between the Omani Musandam Peninsula to the south and Iran to the north (see Figure 1). It is the only maritime passage from the Persian Gulf to the Arabian Sea, and has become one of the world’s most significant oil shipping areas – its increased importance coinciding with the rapid expansion of oil production in the Persian Gulf beginning in the 1950s. It is now the primary export route for oil produced by Bahrain, Kuwait, Iran, Iraq, Qatar, Saudi Arabia and the United Arab Emirates and one of the busiest oil routes globally, with approximately 25 percent of the world’s total oil and liquified natural gas passing through the Strait.

The Strait of Hormuz has the legal status of a strait used for international navigation under Part III of the 1982 United Nations Convention on the Law of the Sea ('UNCLOS'), which entered into force generally on 16 November 1994. Part III of UNCLOS establishes a regime of 'transit passage' that applies to straits used for international navigation between one part of the high seas or an exclusive economic zone and another part of the high seas or an exclusive economic zone. The Strait is situated in an area of maritime space where the 12 nm territorial sea entitlements of the coastal States of Iran and the Sultanate of Oman ('Oman')overlap - the overlap being most pronounced in the geographic centre of the Strait between Jazh Larak Island (Iran) and Great Quoin Island (Oman).

There is no high seas or exclusive economic zone corridor between the maritime zones of Oman and Iran in this area, which results in the entire Strait falling within the territorial sea jurisdiction3 of the two States – Iran to the north and Oman to the south. A maritime boundary delimitation treaty concluded between the two States in 1974 delimits the continental shelf – not the super-jacent waters - using a geodetic median line spanning 125 nm from the eastern Persian Gulf, through the Strait of Hormuz to the Gulf of Oman. In 1968, Iran and Oman proposed a Traffic Separation Scheme ('TSS') designating shipping lanes in the Strait of Hormuz in order to reduce collisions and improve safety of maritime traffic. The TSS was subsequently adopted by the International Maritime Organisation ('IMO') in 1973 and has, following a modification in 1979, remained in place ever since. It consists of two distinct, 2 nm-wide shipping lanes – one in the north used for inbound maritime traffic, and one in the south for outgoing traffic. A 2 nm wide buffer zone separates the inbound and outbound lanes to reduce the potential for maritime collisions

Contested Legal Status

Although UNCLOS has been in force for over 30 years and has over 140 Contracting Parties, neither Iran nor the United States are Parties to the Convention. Consequently, the provisions of UNCLOS are not binding as treaty-law on either State. However, there is overwhelming support for the view that many aspects of the Convention reflect or codify established rules of customary international law. Accepted customary rules are binding on all States – including Iran and the United States – automatically irrespective of any treaty-based rules and applicable to both Iran and the United States.

With respect to international straits and the special regime of transit passage, a number of States take the view that the provisions of Part III of UNCLOS represent a codification of customary international law. This is because even before the Third Law of the Sea Conference first convened in the early 1970s, the critical importance and unique nature of international straits was well recognized. This view has been endorsed and relied upon by the United States, which has declared in various legal settings over many years that the regime of transit passage under UNCLOS represents the codification of established customary international law.

Notwithstanding the position of the United States and number of other States concerning the legal status of the transit passage regime, significant differences of opinion persist regarding the regime. These differences of view are reflected in a lack of uniformity of practice amongst coastal States bordering international straits. This disparity of practice creates legal ambiguity regarding the status of transit passage under customary international law.

Iran's 'Closure' of the Strait of Hormuz

For over 30 years, Iran has consistently maintained that it is not bound by the regime of transit passage set out in UNCLOS - on the basis that the transit passage provisions of Part III did not reflect established rules of customary international law at the time of the adoption of the Convention. In this regard, Iran has formally, and repeatedly, stated that provisions relating to transit passage in UNCLOS are products of a quid pro quo reached in the negotiation of the Convention as a package and not as a codification of existing customary international law. According to this view, the contractual nature of the provisions of UNCLOS necessitates that only States Parties to the Convention can invoke the right of transit passage vis-à-vis each other.

Iran has consistently adopted the position since the 1950s that the regime of 'innocent passage' applies to the areas of the Strait of Hormuz that fall within its territorial sea jurisdiction. This is based on the provisions of the 1958 Geneva Convention on the Territorial Sea and Contiguous Zone, to which Iran is a Contracting Party. Iran also maintained this position throughout the negotiations at the Third United Nations Law of the Sea Conference held during the 1970s that led to the adoption of UNCLOS. The longstanding rejection of the regime of transit passage by Iran, coupled with the differences between transit passage and the regime of innocent passage are crucially important factors in assessing the legality of Iran's present conduct.

The concept of innocent passage is well established under customary international law, and differs markedly from transit passage. Unlike the regime of transit passage, which prohibits coastal States from suspending passage through international straits, innocent passage applies to territorial waters generally. It also operates to permit foreign vessels to navigate through a coastal State's territorial sea without needing prior permission provided that passage is 'continuous and expeditious and not prejudicial to the coastal state's peace, order, or security'. Passage ceases to be 'innocent' inter alia, where a vessel engages in the use of force, or threats of force, spying or propaganda. Most importantly, a coastal state may legitimately and temporarily suspend innocent passage if it is essential for security, subject to the exception that innocent passage of foreign ships cannot be suspended through straits which are used for international navigation between one part of the high seas and another part of the high seas or the territorial sea of a foreign State. This exception is not applicable to the Strait of Hormuz, as it is not a navigation route between areas of high seas.

These established rules on innocent passage are reflected in Iranian domestic law, including the 1964 Iranian Maritime Code (as amended in 2012), and the 1993 Act on Marine Areas. Both pieces of legislation provide that the regulation of maritime traffic through the Territorial Sea of Iran in the Strait of Hormuz is subject to the regime of innocent passage.

During the period of the Iran-Iraq war from 1980–1988, Iran frequently relied upon the innocent passage regime, and in particular, the right to temporarily suspend innocent passage to protect the security of Iran, to justify threats to close the Strait of Hormuz in the event of any attack from Iraq or the United States. Although Iran did not succeed in closing the Strait completely, it did prevent navigation through those parts of the Strait within the territorial sea of Iran as the conflict escalated and the so-called 'Tanker War' erupted in which both Iran and Iraq imposed undeclared blockades on neutral shipping in the Persian Gulf and Strait of Hormuz.

From the commencement of current hostilities, Iran has maintained that its measures in the Strait do not amount to a total closure, but rather, regulation of passage through the Strait under wartime conditions, together with prior notification, new routing requirements, enhanced monitoring and selective access. This was most recently articulated on 29 April, when Iran released an official statement asserting that it has a right to regulate passage in a restrictive manner during hostilities, particularly where it deems passage to be non-innocent on a case-by-case basis.

US Blockade

As noted above, the United States began enforcing a blockade of Iranian ports on 13 April 2026. Properly understood, a naval 'blockade' is a method of warfare that is designed to prevent the access of vessels and aircraft of all States to and from specific coastal areas that are part of or under the control of an enemy State. Under international law, specific rules govern the conduct of blockades by a 'belligerent'. These rules form part of customary international law and have been set out in the restatement of applicable international law in the San Remo Manual on International Law Applicable to Armed Conflicts at Sea.

Articles 93–108 of the San Remo Manual set out the rules governing blockades generally. The key elements of a legal blockade may be summarised as follows: a blockade shall be declared and notified to all belligerents and neutral States; the declaration shall specify the commencement, duration, location, and extent of the blockade and the period within which vessels of neutral States may leave the blockaded coastline; a blockade must be applied impartially to the vessels of all States; merchant vessels believed on reasonable grounds to be breaching a blockade may be captured, and merchant vessels which, after prior warning, clearly resist capture may be attacked; a blockade must be effective — which is to be determined as a 'question of fact'; and a blockade is prohibited if it has the sole purpose of starving the civilian population or denying it other objects essential for its survival.

The San Remo Manual also addresses the establishment of zones during a blockade which might adversely affect the legitimate uses of defined areas of the sea. These rules make it clear that in the event that such zones are established, it must be as an exceptional measure, and shall not exceed what is strictly required by military necessity and the principles of proportionality with due regard given to the rights of neutral States to legitimate uses of the seas. In addition, where such zones have been established, safe passage through the zone for neutral vessels and aircraft must be provided where normal navigation routes are affected, except where military requirements do not permit. Finally, under Article 27 of the Manual, the rights of transit passage applicable to international straits in peacetime continue to apply in times of armed conflict — including with respect to blockades.

The position under international law is therefore clear — a blockade that has the effect of shutting down an international strait to neutral vessels is illegal.

The US Central Command has stated that in enforcing the blockade, the United States will 'not impede freedom of navigation of vessels transiting the Strait of Hormuz to and from non-Iranian ports.' This clarifies that the United States is framing its conduct as a traditional blockade — that is, as a blockade designed to strangulate the economy of Iran and force it to surrender — rather than a blockade targeting all maritime traffic through the Strait.

Issues of State Responsibility

it is possible that States engaged in the current hostilities have committed wrongful acts affecting transit passage through the Strait of Hormuz from the onset of hostilities on 28 February, consideration must be given to the consequences that arise for those States. Consideration should also be given to remedies that may be available to States in respect of harm caused to their flagged vessels and nationals.

The question of the responsibility of a State for damage caused to private or public vessels and aircraft in transit is not expressly addressed in Part III of UNCLOS. Various proposals concerning compensation for loss or damage to a foreign ship caused by a bordering coastal State (but not other States) were raised during the negotiation of the Convention, but ultimately were not adopted in the final text.

It is however well established that every internationally wrongful act of a State entails the international responsibility of that State under international law. This would include illegal acts of preventing or hampering transit passage or unlawful enforcement measures. In this regard, the rules on State responsibility would apply. The governing rules of State Responsibility are largely reflected in the International Law Commission's Articles on State Responsibility, adopted by the United Nations General Assembly in 2001.

The commission of an internationally wrongful act by a State also gives rise to a range of legal consequences provided for under the law of State responsibility. These include obligations of cessation and non-repetition, which are consequences that apply irrespective of the existence of harm, as well as the consequences requiring full reparation, including restitution, compensation and/or satisfaction. And it is important to note that breaches of a State's obligations do not affect the continued duty of the responsible State to perform the obligation breached.

Under international law, where a vessel has been damaged as a consequence of the wrongful act of another State, the flag-State of the vessel may bring a claim against the State responsible for the wrongful act that has caused damage. The established mechanisms for the pursuit of claims by a flag-State are based on diplomatic protection on behalf of a vessel and its nationals — where the flag-State initiates diplomatic communication, protests the wrongful act, demands cessation and requests reparation for damage to the vessel and those on board. This can also involve the litigation of claims by the flag-State before an international court or tribunal with jurisdiction.

As noted earlier, there have been numerous verifiable reports of disruption, seizure, damage and disruption to vessels (and injuries suffered by crew members) engaged in passage through the Strait of Hormuz since the start of the ongoing hostilities. Such damage to vessels and crew does give rise to State Responsibility, and remedies could be sought by the flag-States of the affected vessels and by States of nationality for individuals injured. In this regard, it is also well-established that the conduct of any organ of a State is to be regarded as an act of that State — including military forces — for the purposes of attributing responsibility.

However, certain difficulties may arise in connection with attribution and causation in view of the extraordinary nature of the crisis in the Strait of Hormuz. Attribution is one of the elements necessary for finding an internationally wrongful act, and all international claims require attribution to establish the responsibility of a particular State under international law. Moreover, where reparations are being sought, it must be shown that the damage for which reparation is claimed has been factually and legally caused by a State. Causation of damage is not a requirement for the determination of responsibility as such, but plays an important role in determining the quantum of reparation.

With respect to damage to vessels engaged in transit through the Strait of Hormuz, based on current information, a plurality of responsible States may have contributed to such damage. This uncertainty increases the difficulty of determining whether and to what extent an individual State's breach of an obligation identified has caused significant harm. In such circumstances, it would be for each injured State to separately invoke the responsibility of every State that it believes has committed an internationally wrongful act resulting in damage to its vessels or individuals. And where several States are responsible for the same internationally wrongful act, the responsibility of each State could be invoked in relation to the specific act. This position has been accepted by the ICJ in a number of cases where it has been alleged that multiple States have committed internationally wrongful acts.