While fighting continued around Aleppo and Damascus, Syria’s largest cities, activists said the most serious violence appeared to be the shelling of a cemetery in the Damascus suburb of Modamiyah, where large crowds had gathered to bury at least some of the 40 bodies found in the basement of a mosque after a raid by a newly formed militia of Alawites, Mr. Assad’s minority sect.

“We knew we would find a massacre after they left,” said Ahmad, an activist in the area.

It was unclear how many of the funeral mourners were killed. But the large number of victims found in the mosque was the third instance in the past week of a mass killing after raids by government troops or their supporters, fueling speculation that the Assad government has begun a new campaign of extrajudicial killings to weaken the opposition’s support among civilians.

The Local Coordination Committees, an anti-Assad activist group, said at least 152 people were killed on Tuesday around the country. That tally, which could not be independently corroborated, included 93 in Damascus and its suburbs, mostly in Modamiyah.

Rebel commanders also reported shelling, bombing and executions by government forces in the Dara’a area near the Jordanian border. The Free Syrian Army, the umbrella insurgent group, reported that rebels had to abandon their positions in Hirak, a town that has been bombed severely in recent days, after exhausting their supply of bullets. “There is no ammunition anywhere in Dara’a,” said Rami, an activist there. Another activist there described the situation in Hirak as simply “hell.”

“It’s the worst moment we’ve seen in the besieged town,” he said. “There has been four days of nonstop shelling; there are 3,000 people hiding in shelters.”

In Geneva, the United Nations refugee agency reported a further sharp rise in the number of Syrians fleeing their country on Tuesday, mostly into Turkey, where 3,500 people crossed into Kilis and Hatay Provinces. The latest arrivals, mostly from Aleppo and its surroundings, have brought the total number of Syrians taking refuge in Turkey to nearly 65,000 in nine camps. The refugee agency said about 40 percent of them arrived in August alone.

Turkey has said repeatedly that it will not take in more than 100,000 refugees, which may be contributing to the recent rush, along with continued fighting in Aleppo and leaflets from the Syrian government encouraging people to flee. At the current rate, Turkey would reach its stated limit around the end of September.