Iran’s Revolutionary Guard says it has seized two oil tankers in the Strait of Hormuz – one British-flagged and the other British owned.

The Stena Impero, which is registered in the UK, was seized by the Iranian Revolutionary Guard in the Strait of Hormuz for “violating international maritime rules”, according to the semi-official Fars news agency.

And a second oil tanker, the Liberia-flagged Mesdar, which is owned and operated by Glasgow-based firm Norbulk, appeared to veer off course towards the Iranian coast, according to its path on the Marine Traffic website.

Cobra, the government’s emergency committee, is meeting in Whitehall to discuss the incident, the BBC reported.

“We are urgently seeking further information and assessing the situation following reports of an incident in the Gulf,” a spokesman for the Ministry of Defence said on Friday.

Foreign Secretary Jeremy Hunt said: “I’m extremely concerned by the seizure of two vessels by Iranian authorities in the Strait of Hormuz.

“I will shortly attend a COBR meeting to review what we know and what we can do to swiftly secure the release of the two vessels – a British-flagged vessel and a Liberian-flagged vessel

“Their crews comprise a range of nationalities, but we understand there are no British citizens on board either ship”.

“Our ambassador in Tehran is in contact with the Iranian Ministry of Foreign Affairs to resolve the situation and we are working closely with international partners,” he said.

“These seizures are unacceptable. It is essential that freedom of navigation is maintained and that all ships can move safely and freely in the region.”

Prime Minister Theresa May’s office declined to comment, Reuters reported.

Relations between Iran and the West have been increasingly strained after Britain seized an Iranian tanker in Gibraltar on suspicion of smuggling oil to Syria in breach of European Union sanctions.

Sir Richard Dalton, former British ambassador to Iran, suggested the owners of the Stena Impero had been “rash” in sailing the tanker through the Strait of Hormuz.

Speaking to Sky News, he said Iran’s supreme leader Ayatollah Ali Khamenei had promised retaliation following the detention of Iran’s Grace 1 tanker in Gibraltar.

Dalton said: “With hindsight, it’s easy to say that this was a somewhat reckless act by the owners, given that there was no British naval vessel in the vicinity.”

He said the Iranians had “lost their cool” despite recent “constructive discussions” over the Grace 1 and added “I don’t think the Iranians will continue to try to seize British vessels given they have got what they want, which is something to hold in a negotiation with Britain about their cargo held, they consider illegally, in Gibraltar”. 

A statement from Stena Bulk said ship manager Northern Marine Management had lost contact with the crew of 23 after “unidentified small crafts and a helicopter” approached the vessel at around 4pm on Friday.

The company said the tanker was in international waters at the time but now appeared to be 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 statement read.

“The priority of both vessel owner Stena Bulk and ship manager Northern Marine Management is the safety and welfare of the crew.

“We are in close contact with UK government authorities.”