International law at maritime chokepoints

This article is authored by Ananya Raj Kakoti, scholar, international relations, Jawaharlal Nehru University, New Delhi.

The United Nations Convention on the Law of the Sea (UNCLOS) establishes distinct regimes for navigation through straits vital to global trade. Articles 37–44 govern transit passage in straits connecting high seas or exclusive economic zones, granting ships and aircraft the right to continuous and expeditious passage without impediment from coastal states. This non-suspendable regime applies to critical chokepoints like the Strait of Hormuz and Bab el-Mandeb, superseding innocent passage where territorial seas overlap.

Maritime (AP)

In contrast, Articles 19–22 define innocent passage through territorial seas, permitting navigation that is not prejudicial to the coastal state's peace, good order, or security. Passage must be continuous and expeditious, excluding activities such as weapons exercises or intelligence gathering. For straits not qualifying for transit passage, Article 45 ensures non-suspendable innocent passage.

A critical technical distinction exists between the two regimes that has major implications for naval operations: Under transit passage, submarines may remain submerged as this constitutes a 'normal mode' of operation for such vessels. Under innocent passage, however, submarines must surface and show their flag. This difference is a persistent source of tension between naval powers, which favour submerged transit as customary right, and coastal states, which seek greater visibility over military movements through their territorial waters. The table below summarises the key distinctions between these two regimes.

Table

For archipelagic sea lanes, such as Indonesia's near Malacca, passage mirrors transit rights but requires designation by archipelagic states. Pollution controls align with international standards, yet States must avoid unjustifiable interference. These rights extend to protecting marine environments, though enforcement remains State-driven.

Notably, there is a growing trend of what may be termed 'environmental lawfare', whereby coastal states invoke Article 21, which permits regulations on pollution and navigational safety, as a pretext for detaining or inspecting vessels for political purposes. Iran and Malaysia have both employed environmental and safety pretexts to assert regulatory leverage over commercial and naval shipping. Whilst UNCLOS permits such regulations in principle, their selective application as instruments of geopolitical pressure sits in an uncomfortable grey zone.

The Strait of Hormuz, bordered by Iran and Oman, falls under transit passage despite lying within territorial seas, ensuring unobstructed flow of approximately 20% of global oil. Bab el-Mandeb, linking the Red Sea to the Gulf of Aden, similarly benefits from Article 37, handling some 12% of world trade.

Malacca and Singapore Straits involve transit passage alongside archipelagic provisions for Indonesia and Malaysia. Coastal States such as Iran cannot suspend passage even amid heightened tensions, as transit passage functions as lex specialis, the specialised legal rule that overrides the general law (lex generalis) of innocent passage in these specific straits. Article 38 prohibits impediments, though ambiguities in the 'normal modes' of navigation, particularly regarding submarines and unmanned vessels, continue to generate interpretive disputes.

UNCLOS prohibits the suspension of transit passage even in conflict, prioritising navigational freedoms above countermeasures. Self-defence under Article 51 of the UN Charter may justify temporary measures in extremis, but blockades in naval warfare require prior notification and proportionality per the San Remo Manual on International Law Applicable to Armed Conflicts at Sea. It bears emphasis that the San Remo Manual is not a treaty; it is a scholarly codification of customary law and best practice. As such, it carries persuasive rather than binding force, which goes a considerable way to explaining why belligerents so frequently disregard its provisions in practice.

Belligerents can interdict enemy vessels or mine straits, yet neutral shipping enjoys protections absent imminent threats. Iran's periodic threats to close the Strait of Hormuz invoke claims of aggression, but UNCLOS prevails over unilateral countermeasures. Coastal States may, however, act against non-innocent passages under Article 19, for instance, those posing a credible security threat, provided they do not wholly suspend the transit passage regime.

A further complication arises from the position of the US. As a non-signatory to UNCLOS, the US nonetheless adheres to the transit passage provisions as customary international law, arguing that these norms have been absorbed into the general corpus of binding rules applicable to all states regardless of treaty ratification. This allows the US to assert and enforce transit rights, including through freedom of navigation operations, without formally accepting UNCLOS jurisdiction, a stance that is simultaneously pragmatic and legally contested.

The Houthi attacks in the Red Sea since November 2023 exemplify chokepoint vulnerabilities, with over 130 strikes on commercial vessels via Bab el-Mandeb, halving Suez Canal traffic and causing a sharp surge in global freight costs. Renewed threats in 2026 amid escalating Iran-related tensions risk full blockades, with material consequences for grain and oil imports across dependent economies.

The Strait of Hormuz has witnessed a series of Iranian seizures and explicit closure threats following US military and sanctions actions, testing the limits of transit passage rights without formally triggering their suspension. Incidents in the Malacca Strait have remained comparatively low-level, centred on piracy rather than State action. Collectively, these events have forced considerable shipping traffic to reroute around the Cape of Good Hope, adding ten to 14 days to voyage times and laying bare the fragility of just-in-time global supply chains.

A particularly significant development is the emergence of Anti-Access/Area Denial (A2/AD) capabilities, precision drones, ballistic missiles, and sea mines, deployed by both State and non-State actors. These technologies allow hostile parties to create what amounts to a de facto blockade without the legal formalisation of one, leaving the international legal framework effectively unable to classify or respond to the threat in real time. The Houthi campaign in the Red Sea is the most prominent contemporary illustration of this phenomenon, and its implications for maritime law are profound and as yet unresolved.

The International Tribunal for the Law of the Sea (ITLOS) affirms coastal duties: 'Coastal States must allow innocent passage of foreign ships but may act against passages that are not innocent,' exercising jurisdiction subject to UNCLOS. It is critical to note, however, that ITLOS only has jurisdiction where both parties to a dispute have consented, either directly or through ratification of UNCLOS. This limitation renders the tribunal largely irrelevant in disputes involving the US, which has not ratified the Convention, or non-state actors such as the Houthi movement, which falls entirely outside the treaty framework.

IMO Secretary-General Arsenio Dominguez has highlighted the broader geopolitical dimension, warning that ships and seafarers have increasingly become leverage in geopolitical disputes, a phenomenon acutely visible in the Hormuz crisis. UNCTAD's Rebeca Grynspan has similarly cautioned that maritime chokepoints are particularly vulnerable to disruptions, whether climatic, economic, geopolitical, or operational, a warning that the events of 2025 and 2026 have done little to assuage.

UNCLOS lacks real-time enforcement capacity, relying on slow-moving tribunals such as ITLOS, which enables exploitation of legal ambiguity during active crises. Ambiguities in what constitutes 'prejudicial' activities under Article 19, combined with the contested interplay between UNCLOS and UN Charter self-defence provisions, create significant interpretive leeway for States such as Iran, Russia, and China to act in ways that are technically contestable but practically unchallenged.

No rapid-response protocols exist for chokepoint violations. The IMO lacks enforcement powers, and the UN Security Council is routinely paralysed by regional and geopolitical divisions. Non-signatories such as the US adhere customarily but selectively, whilst hybrid threats involving drones, subsea cables, and precision missiles have comprehensively outpaced the drafters' intentions. The de facto blockade problem posed by A2/AD systems is particularly acute: UNCLOS was written for a world of surface ships and conventional naval engagements, not one in which a non-State actor with access to Iranian-supplied drones can effectively close an international strait to commercial traffic.

Regional forums, such as a proposed Gulf Maritime Security Forum, could begin to bridge these institutional voids by fostering cooperation amongst coastal and user states. More ambitiously, an IMO-led Blue Corridor protocol, establishing protected lanes with internationally monitored safe passage guarantees for merchant vessels in active conflict zones, would represent a meaningful structural reform. Yet, enforcement ultimately hinges on power dynamics and political will, underscoring UNCLOS's underlying resilience as a framework even as 2026's dual chokepoint strains test it to its limits.

(The views expressed are personal)

This article is authored by Ananya Raj Kakoti, scholar, international relations, Jawaharlal Nehru University, New Delhi.