US demands Iran release seized oil tanker 'immediately'

The United States on Thursday demanded that Iran immediately release a ship seized off Oman's coast in avowed retaliation for US actions and said it was looking at steps to take.

"The Iranian government must immediately release the ship and its crew. This unlawful seizure of a commercial vessel is just the latest behaviour by Iran or enabled by Iran aimed at disrupting international commerce," State Department spokesman Vedant Patel told reporters.

Iran seized a tanker with Iraqi crude destined for Turkey on Thursday in retaliation for the confiscation last year of the same vessel and its oil by the United States, Iranian state media reported, a move likely to stoke regional tensions.

The seizure of the Marshall Islands-flagged St Nikolas coincides with weeks of attacks by Yemen's Iran-backed Houthi militias targeting Red Sea shipping routes.

"After the theft of Iranian oil by the United States last year, St Nikolas tanker was seized by Iran's Navy this morning with a judicial order ... it is en route to Iranian ports," the semi-official Fars news agency reported, citing a statement by the Navy.

The St Nikolas, was seized by the United States last year in a sanctions enforcement operation when it sailed under a different name, Suez Rajan. Following the move, Iran warned the US that it would "not go unanswered".

The St Nikolas was boarded by armed intruders as it sailed close to the Omani city of Sohar, according to British maritime security firm Ambrey, and its AIS tracking system was turned off as it headed in the direction of the Iranian port of Bandar-e-Jask.

The ship loaded 145,000 metric tonnes of oil in the Iraqi port of Basra and was heading to Aliaga in western Turkey via the Suez Canal, its operator Empire Navigation told Reuters, adding that it had lost contact with the vessel.

While Yemen's Houthis have since October attacked commercial vessels in the Red Sea to show support for Palestinian militant group Hamas in its fight against Israel, those incidents have been concentrated on the Bab Al Mandab Strait, to the southwest of the Arabian Peninsula.

Thursday's incident is located closer to the Strait of Hormuz, between Oman and Iran.

The vessel is manned by a crew of 19 including 18 Filipino nationals and one Greek national, the operator said, adding it was chartered by Turkish oil refiner Tupras.

The United Kingdom Maritime Trade Operations (UKMTO) authority said earlier on Thursday it had received a report that a vessel located around 50 nautical miles east of Oman's coast was boarded by four to five armed persons.