The problem has become so dire in recent weeks that opposition groups like the Syrian National Council and the Local Coordination Committees have called for restraint by their own supporters, fearing that the problem could spiral out of control.

“We call on the families and relatives of people kidnapped not to be drawn into acts of revenge, which will cost them and their families and pose great dangers to the whole community,” the Local Coordination Committees said in a statement last month.

Monday’s bloodshed appeared the worst so far.

Mr. Saleh, in an account confirmed by an opposition group, said 32 bodies were delivered to the National Hospital in Homs on Monday morning. Kidnappings and killings continued through the day, and Mr. Saleh and other activists said 11 more people had been killed. By nightfall, the 36 bodies were dumped in the square in Al Zahra, an Alawite neighborhood, he said. Several residents said the killings grew worse after a report on Monday that Syria had agreed, with conditions, to accept the entry of monitors from the Arab League.

“There’s chaos, random killing and many killed unintentionally,” Mr. Saleh said.

The accounts from Homs came against a backdrop of rising pressure on the Syrian government, which finds itself more isolated than at perhaps any time in the four decades the Assad family has ruled the country. Leaders with the Syrian National Council met for the first time on Tuesday with Secretary of State Hillary Rodham Clinton, in the highest-level contact the United States has made with the Syrian opposition.

In Cairo, the secretary general of the Arab League, Nabil al-Araby, warned that Syria might face more steps beyond the sanctions imposed last month by the league. “The pressure is going on until the killing stops,” he said in an interview.

He said that an Arab League committee was weighing unspecified further actions, but that he hoped the current penalties would be enough “to change the course” there. “We hope this crisis will end soon and the Syrian people will have a voice in deciding their own future,” he said.

After a six-week absence, the American ambassador, Robert S. Ford, returned to Damascus. The State Department withdrew Mr. Ford over what it described as threats to his safety after his high-profile visits to Syrian cities and meetings with dissidents.