Iran captured an oil tanker off the coast of Oman, heightening tensions in the world’s most important trade lane for global crude supply. 

It seized the St Nikolas “in retaliation for the theft of oil by the US,” Iran’s semi-official Mehr reported. The ship was previously known as the Suez Rajan, which was involved in a high profile American sanctions bust-up that ultimately led to the removal of 1 million barrels of Iranian oil. 

The vessel is being transferred to an undisclosed Iranian port for delivery to authorities, Mehr said. 

While the seizure marks a response to the events surrounding the Suez Rajan last year, the incident brings Iran more directly into the shipping turmoil that’s gripped the Middle East. There have been a number of attacks on ships in the Red Sea over the past two months, primarily by Iran-backed Houthi militants, forcing many merchant vessels to avoid the route and sail thousands of miles around Africa instead. The US and its allies are weighing options for retaliation.

Four to five people in military-style uniforms and black masks boarded the ship, the UK Maritime Trade Operations said. The vessel had loaded about 1 million barrels of crude at the Iraqi port of Basrah for Turkish oil company Tupras and was heading to the country via the Suez Canal.

Oil prices rose as much as 2.3% in London. Crude has been relatively steady since the tensions began as supply hasn’t been directly affected by the tensions in the region. 

Iran had a court order to seize a ship, the country’s semi-official Tasnim agency reported. The vessel’s owner, Empire Navigation, confirmed it had lost contact with the tanker and that it had notified the relevant authorities. Empire renamed the ship around the time it entered a deferred prosecution agreement with the US last year.

Tupras said the St Nikolas shipment was from Iraq’s state oil company SOMO.

The hijacking comes just after American and British jets and warships shot down 18 drones and three anti-ship missiles following the biggest Houthi attack in the Red Sea. US Secretary of State Antony Blinken said there would be consequences and UK Defence Secretary Grant Shapps warned the Houthis to “watch this space.”