Iranian Revolutionary Guards forces boarded a Marshall Islands-flagged cargo ship in the Gulf yesterday after patrol boats fired warning shots across its bow and ordered it deeper into Iranian waters, US officials said.

US planes and a destroyer were monitoring the situation after the vessel, the MV Maersk Tigris, made a distress call in the Strait of Hormuz, one of the world’s most important oil shipping channels.

Oil prices rose by 60 cents on the news, with Brent futures, the global oil benchmark, rallying as high as $65.49 before falling back to around $64.70.

The ship was seized as Teheran inches closer to a final deal with major powers on its nuclear programme. At the same time it faces escalating tension with Gulf Arab powers over the conflict in Yemen, where jets from a Saudi-led coalition bombed Sanaa airport yesterday to block a plane Iran said was carrying aid. Iranian officials sought to play down the ship seizure, saying it was a civil matter with no military or political dimension, but the Pentagon described the move as an apparent provocation.

It was not clear what defence obligation Washington has towards the Marshall Islands, a small Pacific island nation.

Reuters tracking data showed the Maersk Tigris, a 65,000-ton container ship, anchored off the Iranian coast between the islands of Qeshm and Hormuz. It had been listed as sailing from Saudi Arabia’s Red Sea port of Jeddah, bound for the United Arab Emirates port of Jebel Ali in the Gulf.

Iran’s state news agency Irna quoted a source in the Islamic Revolutionary Guards Corps (IRGC) as saying naval units from the Guards force seized the vessel and its 34 crew.

The company managing the vessel told a Danish news channel there were 24 crew members, mostly from eastern Europe and Asia.