New Delhi: The deaths of three Indian seafarers aboard the tanker MT Settebello following a US strike have brought a long-running legal question into focus: when, if ever, can a military power lawfully attack a merchant vessel in international waters?
That question has become pressing after US Central Command (CENTCOM) struck three commercial tankers this week off the coast of Oman—Marivex, Settebello, and Jalveer—after they allegedly failed to comply with US military directions and violated an active US naval blockade of Iran's ports.
Washington maintains that the strikes were lawful acts of maritime enforcement. Critics argue that they instead risk eroding one of the foundational principles of international humanitarian law: that civilian merchant shipping is protected from attack.
The strikes have led to renewed scrutiny on the legal basis for targeting merchant vessels, the authority under which the US is conducting its campaign against Iran, and Washington's own historical approach to civilian shipping during maritime conflicts.
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The US blockade
The attacks on the commercial tankers come amid escalating tensions surrounding Iran and the Strait of Hormuz, a critical waterway through which roughly a fifth of the world's seaborne oil passes. Iran has effectively closed the strait since the beginning of its conflict with Israel and the US in late February this year.
Following the breakdown of negotiations with Tehran and the widening regional conflict, the US announced a maritime blockade on 13 April, intended to target vessels carrying Iranian oil. According to CENTCOM, ships attempting to transport Iranian oil or breaching blockade restrictions would be intercepted and disabled by US forces.
The three tankers struck this week—two flying the Palau flag and one registered in Guinea-Bissau—were all accused by US authorities of attempting to move Iranian oil through restricted waters or failing to comply with instructions from American forces. The targeted strikes at the engine room of the Settebello occurred “after the crew repeatedly failed†to follow directions, CENTCOM said in a post on X.
The Indian government Wednesday summoned US Charge d'Affaires Jason Meeks to register its strong condemnation of the attack on Settebello and seek an explanation for the strike.
“We condemn the attack on the commercial vessel Settebello off the coast of Oman, earlier today… the continuing incidents of attacks on shipping in the region are deeply worrisome and a direct result of the ongoing conflict,†the Ministry of External Affairs said in a statement.
The three Indians killed aboard the Settebello are the first reported fatalities since the US blockade went into effect in mid-April.
For New Delhi, the strikes highlight a growing vulnerability. Indians constitute one of the largest maritime workforces in the world, accounting for roughly 12% of global seafarers. Thousands of Indians work aboard foreign-flagged vessels that traverse some of the world's most important, and volatile, waterways—leaving them susceptible to conflicts beyond India's shores.
What does international law say?
At the centre of the debate is a fundamental principle of maritime law: merchant vessels are presumed to be civilian objects and are therefore protected from attack.
Under the Law of Armed Conflict at Sea, the body of international law governing naval warfare, civilian merchant ships enjoy protection. However, the legal framework changes during armed conflict. In wartime, the law of naval warfare permits attacks on merchant vessels if they become legitimate military objectives.
This principle is reflected in the 1994 San Remo Manual on International Law Applicable to Armed Conflicts at Sea, a widely cited restatement of customary naval warfare law. The manual states that “merchant vessels and civil aircraft are civilian objects unless they are military objectivesâ€.
A merchant vessel can lose its protected status if it directly contributes to military operations: by carrying troops or military cargo, gathering intelligence, acting as a naval auxiliary, or refusing lawful interception.
The US is apparently utilising this logic to justify the strikes against commercial ships.
Washington argues that the three tankers it struck were transporting Iranian oil that would help support Tehran's military activities, thereby making them legitimate targets.
The opposing view is that transport of commercial oil—even oil originating from a sanctioned nation—is not necessarily equivalent to participating in military operations. Under this interpretation, merchant vessels remain civilian objects unless they are directly integrated into a war effort.
In the latter case, attacks on such vessels could violate the principle of distinction: a cornerstone of international humanitarian law requiring combatants to distinguish between civilian and military targets.
The central legal question, then, is whether the vessels had lost their civilian status and become lawful military objectives.
Historical precedent
The debate is also shaped by how Washington has approached similar maritime conflicts in the past, and by the legal justification it has offered now for its campaign against Iran.
On 3 June, the US House of Representatives passed a War Powers Resolution seeking to limit US President Donald Trump's ability to continue military operations against Iran without congressional authorisation. While the resolution is unlikely to become law, it reflects growing concern among lawmakers over the legal basis of the campaign.
The Trump administration has maintained that its actions constitute limited military operations and maritime enforcement rather than a formally declared war—a significant distinction because many of the legal rules governing naval blockades and attacks on merchant shipping were developed in the context of recognised armed conflicts between states.
Historically, the US has generally favoured interception, boarding, seizure and escort operations over direct attacks on commercial shipping.
During the Iran-Iraq Tanker War of the 1980s, for example, Washington largely positioned itself as a defender of freedom of navigation. Through Operation Earnest Will, the US Navy escorted commercial vessels through the Persian Gulf and repeatedly condemned attacks on neutral merchant shipping.
Under the Trump administration, however, Washington seems to have shown greater willingness to use coercive maritime enforcement against vessels accused of evasion.
Last year, US forces conducted targeted strikes against vessels suspected of involvement in illicit petroleum shipments and sanctions violations off the Venezuelan coast. The administration characterised such action as legitimate enforcement measures, while critics viewed them as interference with civilian maritime commerce.
The strikes in the Strait of Hormuz appear to be a continuation of this logic: vessels helping sustain adversarial regimes can become lawful targets if they refuse interception or ignore orders from US naval forces.
The incidents this week could become a defining case for future maritime warfare—and for the protections provided to civilian seafarers navigating some of the world's most dangerous waters.
Kyra Menon is an intern at ThePrint
(Edited by Nida Fatima Siddiqui)
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