The US has closed its embassy in Damascus in a move which increased diplomatic pressure on the Syrian regime as President Barack Obama declared he opposed military intervention.
The withdrawal on Monday of the ambassador Robert Ford and the 17 remaining staff comes amid increasingly brutal attempts by Syrian security forces to put down uprisings in Homs and other cities.
Britain also recalled its ambassador on Monday over what the foreign secretary, William Hague, called the "doomed" regime's "murderous" behaviour, but its embassy remains open.
US state department spokeswoman Victoria Nuland said the move reflected "serious concerns that our embassy is not protected from armed attack". Those concerns were heightened by two car bomb attacks on state security offices in Damascus last month.
"The situation in and around Damascus is becoming increasingly violent, reflecting the fact that the regime is increasingly losing control of the situation because it itself has resorted to violence rather than dialogue," said Nuland.
The state department said that Ford will head the "Syria team" from Washington and that the Syrian embassy in the city remains open with a charge d'affaires so that diplomatic contact can be maintained. Poland will represent US consular interests in Syria.
In the face of calls for stronger action after Russia and China vetoed a UN security council resolution targeting the Bashar Assad's government, Obama said he did not favour replicating the Nato bombing campaign that helped topple Moammar Ghaddafi in Libya in part because of a lack of consensus among the major powers.
He told NBC that a negotiated resolution to the conflict in Syria – where the latest government assault on Homs has killed dozens of people – is possible.
"I think it is very important for us to try to resolve this without recourse to outside military intervention. I think that's possible," he said. "The Assad regime is feeling the noose tightening around them. This is not going to be a matter of if, it's going to be a matter of when."
Asked about parallels with Libya, Obama said the situation was different in part because there is not the kind of unity among the major powers in dealing with Syria.
"I said at the time with respect to Libya that we would be making these decisions on a case by case basis based on how unified the international community was, what our capacities were," Obama said.
"But we have been relentless in sending a message that it is time for Assad to go, that the kind of violence we've seen exercised against his own people over this weekend and over the past several months is inexcusable. But not every situation is going to allow for the kind of military solution we saw with respect to Libya."
On Saturday, Obama accused the Syrian government of an "unspeakable assault against the people of Homs" and called on Assad to "step aside and allow a democratic transition to proceed immediately".
Obama's comments follow sharp criticism in the US, Europe and the Arab world of Russia and China for vetoing the UN security council resolution calling on Assad to step down.
On Monday, America's UN ambassador Susan Rice said China and Russia were running the risk of suffering the same sort of international isolation as Assad because of their decision to block a security council vote embracing an Arab League solution for the Syrian crisis.
Rice said she thinks both Moscow and Beijing "will come to regret" their votes Saturday against the Arab League-sponsored resolution aimed at moving Assad in the direction of a peaceful transition to democracy in his violence-wracked country.
US secretary of state Hillary Clinton also denounced the vetoes as a travesty. On Sunday, she called for "friends of democratic Syria" to rally against Assad's regime, previewing the possible formation of a group of like-minded nations to coordinate assistance to the Syrian opposition.
Nuland said that the US is looking to persuade other countries to increase sanctions and pressuring those countries selling weapons to the regime in Damascus.
"In a situation where the security council has been blocked from acting in support of the Arab League plan in support of defence of the democratic path for Syria, we're going to have to take measures outside the UN" to keep the diplomatic pressure on Assad.