The UK and the United States have pulled diplomatic officials from Syria as the violence there continues to worsen, it was announced on Monday.
British Foreign Secretary William Hague told the Commons that he had recalled the UK's ambassador to London.
Hague told MPs that the humanitarian situation in Syrian cities was deteriorating, and said there was a "grave danger of it escalating further".
He also added his voice to the chorus of international outcry over Russia and China's decision to veto a draft UN resolution calling for an end to the clampdown by Syrian president Bashar al-Assad.
Meanwhile President Obama recalled the US ambassador to Syria and closed its embassy in Damascus, the State Department said on Monday.
It was also reported by the Reuters news agency that Obama had signed an executive order blocking all assets in the United States held by the Syrian government.
In a statement the US said that Ambassador Robert Ford and other officials had left the country as violence escalated in several cities.
"The recent surge in violence, including bombings in Damascus on 23 December and 6 January, has raised serious concerns that our embassy is not sufficiently protected from armed attack," spokesperson Victoria Nuland said.
"We, along with several other diplomatic missions, conveyed our security concerns to the Syrian Government but the regime failed to respond adequately."
More than 5,400 people have been killed in Syria since protests against President Bashar al-Assad's government began last March, according to the UN.
The US has long insisted that Assad step down and end attacks against his own people.
US Ambassador Susan Rice told the UN Security Council on 4 February the country was "disgusted” after a resolution that backed an Arab League peace plan to end violence in Syria and called for President Assad to stand down was vetoed by China and Russia.
“The United States is disgusted that a couple of members of this council continue to prevent us from fulfilling our sole purpose here — addressing an ever-deepening crisis in Syria and a growing threat to regional peace and security,” Rice said after the council voted.
More than 200 people were killed this weekend in the worst period of sustained bloodshed of the 11-month uprising.
BBC journalist Paul Wood, who is inside the city of Homs, described "pretty constant shelling", adding rocket launchers were also being used. He also said there were unverified claims a field hospital had been targeted.
In the full statement announcing the suspension of its embassy's operations, the US State Department said:
The United States has suspended operations of our Embassy in Damascus as of February 6. Ambassador Ford and all American personnel have now departed the country.
The recent surge in violence, including bombings in Damascus on December 23 and January 6, has raised serious concerns that our Embassy is not sufficiently protected from armed attack. We, along with several other diplomatic missions, conveyed our security concerns to the Syrian Government but the regime failed to respond adequately.
Ambassador Ford has left Damascus but he remains the United States Ambassador to Syria and its people. As the President’s representative, he will continue his work and engagement with the Syrian people as head of our Syria team in Washington. Together with other senior U.S. officials, Ambassador Ford will maintain contacts with the Syrian opposition and continue our efforts to support the peaceful political transition which the Syrian people have so bravely sought.
As the Secretary told the Security Council on January 31, we continue to be gravely concerned by the escalation of violence in Syria caused by the regime's blatant defiance of its commitments to the action plan it agreed to with the Arab League. The deteriorating security situation that led to the suspension of our diplomatic operations makes clear once more the dangerous path Assad has chosen and the regime’s inability to fully control Syria. It also underscores the urgent need for the international community to act without delay to support the Arab League’s transition plan before the regime’s escalating violence puts a political solution out of reach and further jeopardizes regional peace and security.