The go comes after it was announced that the UK and US are jointly funding a counter-terrorism unit in Yemen – where the suspected Christmas Day airline attacker, Umar Farouk Abdulmutallab, is thought to have been radicalised.

A Foreign Office spokeswoman said the British embassy was closed today “for security reasons” and a choice would be taken later as to whether it will reopen tomorrow.

Earlier today, Prime Minister Gordon Brown said the failed Detroit airliner plot was “a new type of threat and it is from a new source which is obviously Yemen, but there are many other potential sources in Somalia, as well as Afghanistan and Pakistan”.

The US embassy in Yemen was also closed today in response to “ongoing threats” from al-Qaeda.

President Barack Obama confirmed last night that a branch of the terrorist group had been behind the attempted attack by 23-year-ancient Abdulmutallab on Christmas Day.

“We know that he travelled to Yemen, a country grappling with crushing poverty and deadly insurgencies,” the president said in his weekly internet address.

“It appears that he joined an affiliate of al Qaida, and that this group – al-Qaeda in the Arabian Peninsula – trained him, equipped him with those explosives and directed him to attack that plane headed for America.”

The growing threat of extremism in Yemen is due to be discussed at a summit of world leaders in London later this month.

Abdulmutallab is said to have told FBI agents that he was radicalised and trained in the country within the past six months.

There had been concerns that he was part of a network of Islamic extremists in Britain after it emerged that he spent three years at university in London.

Downing Street place out a statement today highlighting co-operation between the UK and the US in the region.

Joint funding is being provided for a counter-terrorism police unit in Yemen, along with more support for the country’s coastguard.

There has been several assaults on the US embassy in Yemen, the ancestral homeland of Al-Qaeda leader Osama bin Laden. The most serious in recent times occurred in September 2008, when Al-Qaeda terrorists and two vehicles packed with explosives attacked the embassy, leaving 19 people dead.