UK Foreign Secretary, Jeremy Hunt, has warned Iran will face "serious consequences" if it does not release a British-flagged oil tanker which was detained in the Strait of Hormuz.
The foreign secretary attended a meeting of the British government's emergency committee Cobra on Friday night amid escalating tensions in the region.
The Swedish owners of the Stena Impero confirmed the vessel was approached by unidentified small crafts and a helicopter as it passed through the Strait of Hormuz on Friday at around 4pm GMT.
The Iranian Revolutionary Guard told state TV last night they had seized the ship for "violating international maritime rules".
A second oil tanker, the British-operated, Liberia-flagged Mesdar, was also boarded by armed Iranian guards before being allowed to continue its voyage, its Glasgow-based owner Norbulk said.
This morning, an Iranian official told Fars News the Stena Impero had been involved in an accident with an Iranian fishing boat and had "ignored" the boat's distress call.
The tanker is reported to be at Iran's Bandar Abbas port, with all 23 crew members still on board. Fars said they would remain there until the end of the investigation. It is understood none are British.
The head of Ports and Maritime Organisation in southern Hormozgan province, Allahmorad Afifipour, told Fars there were 18 Indian crew members and five others from Russia, the Philippines, Lithuania and elsewhere.
There were no reports of injuries.
Mr Hunt said Iran's actions were "completely unacceptable", but stressed he wanted a diplomatic solution to the incident.
