A British-flagged oil tanker has been seized in the Gulf by the Iranian Revolutionary Guard.
The owners of the Stena Impero, which was bound for Saudi Arabia, said they have been unable to contact the vessel and it is heading north towards Iran.
The company said there are 23 personnel on board and it was approached by unidentified small crafts and a helicopter in the Strait of Hormuz.
The British Foreign Office says it is urgently looking into the reports.
The government's emergency committee, Cobra, is meeting in Whitehall to discuss the incident.
This latest development comes amid heightened tensions between the UK and Iran.