BEIRUT, Lebanon — The United States joined with 10 other nations to expel top Syrian diplomats on Tuesday, increasing international pressure on President Bashar al-Assad. In Damascus, the United Nations envoy said the uprising had reached “a tipping point” after a massacre of more than 100 villagers, nearly half of them children.

In his remarks, Kofi Annan, the envoy for the United Nations and the Arab League, was dismissive of the Syrian government refrain that outsiders were responsible for the bloodshed. After meeting with Mr. Assad on Tuesday, he called on the Syrian president to take “bold steps” to end the fighting and salvage a peace plan that has been increasingly criticized for failing to end the violence.

“The Syrian people do not want their future to be one of bloodshed and division,” Mr. Annan said after two days in Damascus. “Yet the killings continue, and the abuses are still with us today.”

Even while Mr. Annan made his appeals, in a coordinated action at least 11 nations expelled the Syrian diplomats to express outrage over the deaths of 108 villagers in Houla, near Homs, on Friday. But Syria’s diplomatic chastening did little to sway its public posture, demonstrating the limited leverage of the West as it continues to look to Mr. Annan and a peace initiative that has shown no sign of ushering in an end to more than 14 months of violence.