A British-flagged oil tanker has been seized in the Gulf by the Iranian Revolutionary Guard, Iran media say.
The owners of the Stena Impero, which was bound for Saudi Arabia, say they have been unable to contact the vessel and it is “heading north towards Iran”.
The company says there are 23 personnel on board and it was approached by “unidentified small crafts and a helicopter” in the Strait of Hormuz.
The Foreign Office 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.
Stena Bulk, the vessel owner, and ship manager Northern Marine Management confirmed the UK-registered Stena Impero was approached at around 16:00 BST on Friday while it was in international waters.
A statement said: “We are presently unable to contact the vessel which is now heading north towards Iran.
“There have been no reported injuries and their safety is of primary concern to both owners and managers.”
Tensions between the UK and Iran flared up earlier this month when Royal Marines seized an Iranian tanker which was suspected of breaking EU sanctions.
The UK suspected Grace 1, detained on 4 July near Gibraltar, was carrying oil bound for Syria.
In response to the seizure, Iran threatened to seize a British oil tanker.
On 9 July, the UK raised the threat to British shipping in Iranian waters in the Gulf to “critical” – the highest level.
A day later, Iranian boats attempted to impede a British oil tanker in the region, before being warned off by a Royal Navy ship, according to the Ministry of Defence.
Iran denied any attempted seizure.