Syrian government forces pressing a ferocious crackdown shelled the central city of Homs on Monday, opposition activists said, destroying a makeshift clinic and leaving dozens dead in a town that has been a hotbed of antigovernment resistance.
The government of President Bashar Assad denied any involvement in an assault and said "terrorists" had attacked its forces.
In Washington, the State Department announced that it was suspending operations at the U.S. Embassy in the Syrian capital of Damascus because of "growing safety risks." Ambassador Robert Ford and all other U.S. personnel have left the country.
The department said in a statement that the recent increase in violence, including bombings in Damascus on Dec. 23 and Jan. 6, had raised serious concerns about the safety of the embassy and that Syrian authorities had failed to respond adequately to requests for more security help.
Ford will continue to serve as U.S. representative to Syria from Washington, the department said.
Violence has been escalating in Syria as government forces confront army defectors and other armed rebels seeking Assad's ouster. Homs has long been the scene of street battles, but the opposition says government attacks have intensified in recent days.
Late Friday, the opposition says, the government unleashed a mortar barrage on Homs' Khaldiyeh neighborhood, killing about 200 people in the heaviest one-day casualty toll of the nearly 11-month-old conflict. On Monday, opposition activists say, the bombardment started shortly after dawn in Bab Amro, another bastion of anti-Assad resistance.
"It's a massacre in the true meaning of the word," a witness, who asked not to be identified for security reasons, said by telephone.
Among the structures destroyed, activists said, was a field hospital where the wounded were being treated.
At least 74 people were killed throughout Syria on Monday, including 47 in Homs, according to the Local Coordination Committees, an opposition coalition. The group reported other clashes and killings in the suburbs of Damascus. There was no way to verify the reports.
Opposition groups said the collapse on Saturday of a United Nations resolution endorsing a plan for Assad to cede power has emboldened Syrian authorities to push ahead with their crackdown. Russia and China vetoed the measure, calling it a strike against Syria's sovereignty. Diplomats warned Syria not to take advantage of the outcome to bolster attacks.
"The lack of agreement in the Security Council gives no license to the Syrian authorities to step up attacks on the Syrian population," U.N. Secretary-General Ban Ki-moon said in a statement.
The Syrian government denies carrying out any such attacks.
The State Department again urged world powers to support a diplomatic plan laid out by the Arab League, which calls for Assad to turn over power to a deputy to open the way to a democratic government.
Top Russian envoys, including Foreign Minister Sergei Lavrov, were expected in Damascus on Tuesday to meet with Assad. Moscow has said it wants to encourage negotiations to end the bloodshed.
Marrouch is a special correspondent.
Times staff writer Paul Richter in Washington contributed to this report.