LONDON, July 19 (Xinhua) -- Britain's Foreign Secretary Jeremy Hunt said Friday night he was "extremely concerned" by the seizure of two naval vessels by Iranian authorities in the Strait of Hormuz in what is being seen as a rise in tensions in the region, which is "unacceptable" to the British government.

The Foreign and Commonwealth Office (FCO) in London said Friday it was urgently looking into the reports.

Hunt and senior politicians and military personnel were attending an urgently called meeting of Britain's emergency response team, known as COBR to discuss what response the U.K. should make.

Hunt said on his social media site: "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."

Concerns were raised after reports were received that the Stena Impero was seized in the Gulf, apparently by Iranian Guard.

A Whitehall source told the Daily Telegraph Friday night: "It does look like it (the Stena Impero) has been hijacked. Ships don't follow that pattern. It turned right and straight into Iranian waters. It is really concerning that this has happened."

"It looks on the face of it as though the Iranian Revolutionary Guard have boarded and taken a UK-flagged ship," the report added.

Media reports in London said the owners of the Stena Impero, which was bound for Saudi Arabia, said they had been unable to contact the vessel, adding it was heading north towards Iran.

A maritime tracking website also reported a second tanker with UK links has made a sharp turn towards Iran, named as the Liberian registered MV Mesdar which is British owned, according to media reports.

Northern Marine, a Scottish-based subsidiary of the ship's Swedish owner Stena AB, confirmed that a "hostile action" had preceded the vessel's change of course on Friday afternoon.

The owners confirmed it was approached at around 16:00 BST on Friday while it was in international waters.

A statement from the owners 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."

In a statement Friday night, Bob Sanguinetti, CEO of the UK Chamber of Shipping, said: "We condemn unreservedly the capture of Stena Impero as she transited the Strait of Hormuz earlier today. The action by those involved is in violation of international regulations which protect ships and their crews as they go about their legitimate business in international waters.

"Our priority is for the safety and welfare of the crew. We call on the UK Government to do whatever is necessary to ensure their safe and swift return."