BEIRUT - The United States joined with 10 nations in expelling top Syrian diplomats Tuesday, increasing international pressure on President Bashar 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 UN and the Arab League, was dismissive of the Syrian government refrain that outsiders were responsible for the bloodshed. After meeting with 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,’’ Annan said after two days in Damascus. “Yet the killings continue and the abuses are still with us today.’’

Even while Annan made his appeals, at least 11 nations, in a coordinated action, 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 Annan and a peace initiative that has shown no sign of ushering in an end to more than 14 months of violence.

In Washington, in the midst of a heated political campaign for the presidency, the deterioration in Syria has prompted Republican denunciations of President Obama, but few alternative ideas. There is little appetite among most Americans for a military campaign, officials said, and there is concern that if the government of Syria falls it could be replaced by an extremist Islamist leadership.

With little room to maneuver, the United States joined Australia, Canada, Britain, Bulgaria, France, Germany, Italy, the Netherlands, Switzerland and Spain, to oust Syrian diplomats. In Washington, the State Department said the United States was evicting the Syrian charge d’affaires, Zuheir Jabbour, giving him 72 hours to leave the country.

Despite the tough talk, there remained little support for any manner of armed intervention, which is what many Syria analysts and exiles believe is required to make Damascus budge. At the White House, spokesman Jay Carney said that military intervention was not the right course of action at this time because it would provoke wider carnage and chaos.

William Hague, Britain’s foreign secretary, said three Syrian diplomats had been given a week to leave. The expulsions were meant to “send a stark signal to President Assad and those around him that their actions have consequences and that they cannot act with impunity.’’

The UN Security Council condemned Syria at an emergency meeting on Sunday, blaming it at least partly for the Houla massacre, saying it shelled civilian neighborhoods with heavy artillery. The council was scheduled to meet again on Wednesday on Syria. But divisions with Russia have prevented more weighty international measures like an arms embargo.

Annan said he appealed to Assad in their meeting Tuesday for the Syrian government, as the stronger party, to move first to implement the six-point peace plan in its entirety. He also appealed to the opposition to lay down its arms.

Syria maintained its standard line even as the UN revealed new details about the massacre that pointed blame at the government.

In Geneva, the Office of the High Commissioner for Human Rights announced that most of the victims were summarily executed in their homes.

The initial finding by UN monitors, corroborated by other sources, showed that tank and artillery fire accounted for fewer than 20 of the 108 people confirmed dead in the Houla region, said Rupert Colville, spokesman for the UN human rights commissioner. Most of the rest were shot or stabbed, he said, adding, “At this point it looks like entire families were shot in their houses.’’