The crisis in relations between Iran and Western Government have hit a new low after a British oil tanker was seized.
Iran's Revolutionary Guard confirmed it had seized a British vessel in the Strait of Hormuz on Friday.
A statement from Stena Bulk, which owns the commercial ship, confirmed 23 seafarers on board.
The Government said it is "urgently" seeking information after reports a British-flagged oil tanker has been seized in the Strait of Hormuz near Iran.
The semi-official Fars news agency reported that the Iranian Revolutionary Guard had seized the Stena Impero.
A Government spokesman said: "We are urgently seeking further information and assessing the situation following reports of an incident in the Gulf."
A statement from Stena Bulk, the company which owns the tanker, said the firm had lost contact with the crew of 23 after it was approached by "unidentified small crafts and a helicopter" at around 4pm.
The statement said: "Stena Bulk and Northern Marine Management can confirm that at approximately 1600 BST on 19th July UK registered vessel Stena Impero (built 2018, 49,683 DWT) was approached by unidentified small crafts and a helicopter during transit of the Strait of Hormuz while the vessel was in international waters.
"We are presently unable to contact the vessel which is now heading north towards Iran.
"There are 23 seafarers aboard. There have been no reported injuries and their safety is of primary concern to both owners and managers.
"The priority of both vessel owner Stena Bulk and ship manager Northern Marine Management is the safety and welfare of the crew."
