Some of the staff at the UK's Iranian embassy have been withdrawn from Tehran following yesterday's storming of the building by protesters, the Foreign Office said today.
Prime Minister David Cameron last night warned the regime of Mahmoud Ahmadinejad of "serious consequences" following the attack, which saw hundreds of demonstrators smash windows, torch cars and burn Union flags.
The Prime Minister branded the Iranian government a "disgrace" for failing to protect staff at the embassy and two diplomatic compounds which were ransacked in the capital. Foreign Secretary William Hague is expected to update MPs on the situation in a statement to the House of Commons later today.
Around 24 embassy staff and their dependants are based at the office and residential compounds in Tehran. The Foreign Office this morning confirmed that a number of them were leaving the city today in the wake of the trouble.
An FCO spokesman said: "The Prime Minister and Foreign Secretary have made clear that ensuring the safety of our staff and their families is our immediate priority. In light of yesterday's events and to ensure the ongoing safety, some staff are leaving Tehran."
Asked how many staff were leaving or if the embassy was going to remain open, he added: "We do not comment on our contingency plans and we will make any announcement about our embassy and staff at the appropriate time."
British nationals have been warned against "all but essential travel" to Iran and the small number in the country were told to stay indoors and await advice.
The attacks come two days after the Iranian parliament approved a bill reducing diplomatic relations with Britain following London's support of recently-upgraded US sanctions on Tehran.
The bill - which marks a new low point in diplomatic tensions between London and Tehran - requires Iran and Britain to withdraw their ambassadors from each other's country and reduce representation to the level of charge d'affaires.
It also calls for trade between the two countries to be reduced to "minimum levels".
Last week, the UK announced that it had severed all financial ties with Iranian banks in response to mounting fears over the country's nuclear ambitions.
Chancellor George Osborne said all British credit and financial institutions had to cease trading with Iran's banks from the afternoon of Monday November 21 - the first use of the power to cut off an entire nation's banking sector.
The move was part of a wider international effort by the United States and Canada to put pressure on the Islamic republic, which western governments have accused of seeking to produce nuclear weapons for almost a decade.
Diplomatic tensions were significantly raised earlier this month after the latest assessment by the United Nations' nuclear watchdog warned of Iran's "capacity creep" towards an atomic weapon.
After chairing a meeting of the Government's Cobra security committee yesterday, Mr Cameron demanded prosecution for those responsible for the embassy attack.
"The failure of the Iranian government to defend British staff and property was a disgrace," he said.
"We hold the Iranian government responsible for its unacceptable failure to protect diplomats in line with international law."
The Prime Minster said the British ambassador and all his staff had been accounted for, but "extensive damage" was caused to property.
"The Iranian government must recognise that there will be serious consequences for failing to protect our staff," Mr Cameron added.
"We will consider what these measures should be in the coming days."
Mr Hague spoke to his Iranian counterpart to protest in "the strongest terms" about the attacks.
"While he said he was sorry for what had happened and that action would be taken in response, this remains a very serious failure by the Iranian government," said the Foreign Secretary.
The UN Security Council condemned the attacks "in the strongest terms", while US president Barack Obama called on Iran to hold those responsible to account.
In a statement, the Iranian Ministry of Foreign Affairs voiced "regrets for some of the unacceptable behaviours by few demonstrators that were carried out in spite of the efforts made by the police forces and strengthening the forces to protect the embassy".
The Ministry said it was committed to "safeguard and protect the diplomatic places and personnel" and had ordered an immediate investigation of yesterday's incidents.
"It is conceded that the case will be followed through legal channels and the relevant authorities," said the statement.