Image copyright Reuters Image caption Yemeni patrols have secured streets near the British embassy

All British diplomatic staff in Yemen have been withdrawn to the UK and the embassy closed "due to increased security concerns", the Foreign Office has said.

Dozens of employees were moved to the UK overnight, the BBC understands.

Earlier the United States ordered all its citizens in the country to leave following a terror alert.

Twenty US embassies and consulates in the Middle East and North Africa were closed suddenly on Sunday.

'Not an evacuation'

In a statement the Foreign Office (FCO) added: "Due to increased security concerns, all staff in our Yemen embassy have been temporarily withdrawn, and the embassy will remain closed until staff are able to return."

The BBC's security correspondent, Frank Gardner, said the decision was taken on Monday and that all the staff were currently en route back to the UK.

Officials are describing the action as a "drawdown", rather than an evacuation, our correspondent added.

Similar closures of British missions have recently taken place in the Libyan city of Benghazi and the Syrian capital Damascus.

Explosions

British nationals had previously been advised against all travel to Yemen and those in the country urged to leave immediately.

FCO officials said it was "extremely unlikely" they could be evacuated in the event of the security situation worsening.

The BBC understands Yemeni intelligence services had discovered that tens of al-Qaeda members had arrived in the capital Sanaa over the past few days in preparation for the implementation of a large plot.

Speaking to the BBC's Abdullah Ghorab, a security source described the plot as dangerous, and suggested it was to include explosions and suicide attacks aimed at Western ambassadors and foreign embassies in Yemen, in addition to operations aimed at the Yemeni military headquarters.

Meanwhile, international intelligence agency Interpol said countries should show "increased vigilance", after hundreds of terrorists in Iraq, Libya, Pakistan and six other countries were freed in prison escapes.