US mulls plan to disrupt Iran's oil by halting vessels at sea

President Donald Trump’s administration is considering a plan to stop and inspect Iranian oil tankers at sea under an international accord aimed at countering the spread of weapons of mass destruction, sources familiar with the matter told Reuters.

Trump has vowed to restore a “maximum pressure” campaign to isolate Iran from the global economy and drive its oil exports to zero, in order to stop the country from obtaining a nuclear weapon.

Trump hit Iran with two waves of fresh sanctions in the first weeks of his second-term, targeting companies and the so-called shadow fleet of ageing oil tankers that sail without Western insurance and transport crude from sanctioned countries.

Those moves have largely been in line with the limited measures implemented during former President Joe Biden’s administration, during which Iran succeeded in ramping up oil exports through complex smuggling networks.

Trump officials are now looking at ways for allied countries to stop and inspect ships sailing through critical chokepoints such as the Malacca Strait in Asia and other sea lanes, according to six sources who asked not to be named due to the sensitivity of the subject.

That would delay delivery of crude to refiners. It could also expose parties involved in facilitating the trade to reputational damage and sanctions, the sources said.

“You don’t have to sink ships or arrest people to have that chilling effect that this is just not worth the risk,” one of the sources said.

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“The delay in delivery … instills uncertainty in that illicit trade network.”

The administration was examining whether inspections at sea could be conducted under the auspices of the Proliferation Security Initiative launched in 2003, which aims to prevent the trafficking of weapons of mass destruction.

The US drove that initiative, which has been signed by over 100 governments.

This mechanism could enable foreign governments to target Iran’s oil shipments at Washington’s request, one of the sources said, effectively delaying deliveries and hitting supply chains Tehran relies upon for revenue.

The National Security Council, which formulates policy in the White House, was looking into possible inspections at sea, two of the sources said.

It was unclear if Washington had yet approached any signatories to the Proliferation Security Initiative to test their willingness to cooperate with the proposal.

John Bolton, who was the US lead negotiator for the initiative when it was formed, told Reuters “it would be fully justified” to use the initiative to slow down Iran oil exports. He noted that selling oil was “obviously critical to raise revenue for the government of Iran to conduct both its proliferation activities and support for terrorism.”

The White House National Security Council did not respond to requests for comment.

Iran’s oil and foreign ministries did not respond to separate requests for comment.

Iran has previously stressed that it will not yield to pressure and sanctions imposed by Washington.

Previous attempts to seize Iranian oil cargoes have triggered retaliation by Iran.

The US tried to interdict at least two cargoes of Iranian oil in 2023, under Biden. This prompted Iran to seize foreign ships – including one chartered by Chevron Corp CVX.N, which sent crude prices higher.

The current low oil price environment gives Trump more options to block Iranian oil flows, from sanctions on tanker companies to seizing ships, according to Ben Cahill, an energy analyst at the Centre for Energy and Environmental Systems at the University of Texas.

“I think if prices stay below $75 a barrel, the White House has more latitude to look at sanctions that would affect, you know, supply from Iran and other countries. It would be much harder to do this in a $92 per barrel environment,” Cahill said.