The UK has withdrawn its diplomatic staff from Syria and closed the embassy in Damascus on security grounds, Foreign Secretary William Hague has announced.
Ambassador Simon Collis and his staff left Syria yesterday after it was decided the "deterioration in the security situation" had put their safety at risk.
The decision to suspend operations in Damascus comes after Mr Hague urged those fighting for President Bashar Assad's regime to lay down their arms.
In a written statement to Parliament, Mr Hague stressed the decision to withdraw embassy staff "in no way reduces the UK's commitment to active diplomacy to maintain pressure on the Assad regime to end the violence".
Mr Hague said: "We have maintained an embassy in Damascus despite the violence to help us communicate with all parties in Syria and to provide insight into the situation on the ground.
"Throughout this time we have kept the security situation of our staff and embassy premises under intense and constant review.
"We now judge that the deterioration of the security situation in Damascus puts our embassy staff and premises at risk and have taken the decision to withdraw staff accordingly.
"Our ambassador and diplomatic staff left Syria on February 29 and will return to the UK shortly.
"British nationals who remain in Syria despite our long-standing and consistent message to leave the country should contact the embassy of any remaining EU member state if they require consular assistance."
Mr Hague said the UK would continue to work with the opposition Syrian National Council and support UN and Arab League special envoy Kofi Annan's work.
Yesterday Mr Hague warned that Syrian soldiers would be held to account if they turned their weapons on their fellow countrymen in the expected assault on Homs.
Mr Hague said he was "appalled" at reports that Assad is preparing a full-scale onslaught on the city, which has become a stronghold of dissent against his regime.
He urged Assad to call off any such plans and instead to allow access for humanitarian agencies.
Britain also condemned the refusal by Damascus to allow the United Nations humanitarian affairs and emergency relief co-ordinator Baroness Valerie Amos into the country to assess the scale of suffering caused by the violence.
Responding to reports that troops loyal to Assad were advancing on Homs, Mr Hague said: "I call on those Syrians who are being ordered to attack their fellow citizens to make a choice and to lay down their arms. Those who do not do so will be held to account for their actions.
"Britain will continue to do all it can to bring the greatest possible pressure to bear on the Assad regime until it ceases the violence and repression which is doomed to fail. We will work with the Arab League to ensure a Syrian-led political transition that brings an end to this terrible crisis."
Downing Street today called on Syrian troops not to turn their weapons on civilians.
"There is a choice for those who have taken up arms against innocent civilians," said a Downing Street spokeswoman. "Give up your weapons and we will support you in building a freerSyria, or face the pressure of international opinion."
The spokeswoman said Prime Minister David Cameron will raise the issue of Syria with EU partners at the European Council summit which starts in Brussels today.
"We expect the Prime Minister to underline the fact that we are appalled by the situation and we will work with colleagues across Europe, as well as the Arab League and the UN, in order to bring the greatest possible pressure to bear on the Assad regime and ensure a Syrian-led political transition that brings an end to the terrible crisis," she said.
"What we want to see is an end of the violence and a peaceful resolution.
"Clearly, thousands of people are losing their lives in this terrible situation. Any way forward has got to be through peaceful means. We have got sanctions in place and we want to make sure that those people who have committed atrocities and crimes face up to those crimes."
Asked for the PM's response to the withdrawal of embassy staff, she added: "It is disappointing that we have had to remove staff due to security reasons, but we are going to continue to do what we can to bring the greatest pressure to bear on the Assad regime."
The British Red Cross said it had launched a Syria Crisis Appeal to help provide food, medical supplies and transport for the wounded.
The charity said it had provided more than £500,000 to support humanitarian work in Syria since May last year.
The Syrian Arab Red Crescent and International Committee of the Red Cross (ICRC) have also been helping get food, blankets and medication to thousands of people in at least 20 cities, towns and villages affected by the unrest.
British Red Cross disaster response manager Barry Armstrong said: "The humanitarian situation is critical. People are struggling to get food, to get even basic medical help.
"The ICRC and the Syrian Arab Red Crescent have been working around the clock, often risking their own lives, since this crisis began to help ease the suffering of thousands of Syrian families.
"The British Red Cross has a long-standing partnership with the Syrian Arab Red Crescent and this appeal will support their vital work to bring aid to people affected by this ongoing crisis."
Marianne Gasser, head of the ICRC's delegation in Syria, added: "We are concerned about the consequences of the unrest from a humanitarian viewpoint and about the current deterioration of the situation. The population, particularly the wounded and sick, are bearing the brunt of the violence."
To donate to the Syria Crisis Appeal visit redcross.org.uk/syriacrisis or call 0845 054 7206.