DUBAI: Iranian forces boarded a Marshall Islands-flagged cargo ship in the Gulf on Tuesday after patrol boats fired warning shots across its bow and ordered it deeper into Iranian waters, the Pentagon said.

United States 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.

There was no immediate word from Iranian officials. However, Iran’s Tasnim news agency said the ship incident does not have a military or a political dimension, and is a civil matter, citing an unidentified source.

Saudi-owned Al Arabiya television earlier said an Iranian force fired on and seized a US cargo ship with 34 US soldiers on board, and directed it to the Iranian port of Bandar Abbas. But the Pentagon spokesman said there were no US citizens on board the ship.

The Iranian navy seized a ship on Tuesday at the request of Iran's Ports and Maritime Organisation, the English-language service of Iran's semi-official Fars News Agency also reported. “The ship is a trade vessel and has been seized by the Iranian navy,” said Fars, citing what it called an informed source.

“The ship was seized after a relevant court order was issued for its confiscation,” the source was quoted as saying, referring to differences between the ports organisation and the vessel's owner. It did not identify the owner.

Reuters tracking data showed the Maersk, a 65,000-tonne container ship, off the Iranian coast between the islands of Qeshm and Hormuz. It was listed as sailing from the Saudi port of Jeddah, bound for the United Arab Emirates port of Jebel Ali, although it was still close to the Iranian port of Bandar Abbas at 1530 GMT on Tuesday.

A US government official said the ship was intercepted by the Naval force of Iran's Islamic Revolutionary Guard Corps (IRGC) at 0905 GMT.

The confrontation came amid heightened tensions in the region as Saudi Arabia and its Gulf allies carry out air strikes in Yemen against Houthi rebels, who the allies claim are backed by Iran.

Explore: Fighting intensifies in Yemen.

The US is providing intelligence and aerial refueling for the Saudi-led coalition.

The Pentagon spokesman said the incident occurred when the Maersk Tigris was passing through the Strait of Hormuz. Some 17 million barrels per day (bpd), or about 30 per cent of all seaborne-traded oil, passed through the channel in 2013, according to the US Energy Information Administration (EIA).

Iran has in the past sometimes threatened to block the strait to advance its opposition to sanctions imposed over its nuclear programme.

The channel is a narrow strip of water separating Oman and Iran. It connects the biggest Gulf oil producers, such as Saudi Arabia, with the Gulf of Oman and the Arabian Sea.

At its narrowest point, the strait is 33 kilometres across and consists of 2-mile wide navigable channels for inbound and outbound shipping and a 2-mile-wide buffer zone.