Confronting a scene of congealed blood, scattered body parts, shelled buildings, bullet holes, and the smell of burned flesh, UN monitors in Syria quietly collected evidence Friday of a mass atrocity in a desolate hamlet, more than 24 hours after Syrian forces and government supporters blocked their first attempt to visit the site.

The monitoring team’s journey to Qubeir, filmed and posted online, presented the outside world with the first visual proof from a neutral official source that a horrific crime had occurred there. No corpses were found, and the team’s officials said many of the facts behind the killings, which occurred Wednesday, had yet to be determined.

But it seemed clear that the perpetrators had hastily sought to conceal what had happened, reinforcing suspicions that the successful government attempt to thwart the monitors’ efforts to reach the site Thursday had bought time for a coverup.

Activist groups have accused President Bashar Assad of orchestrating the killings in a campaign to terrorize opponents in Syria’s 16-month uprising against him, which has grown more violent and sectarian in nature despite numerous diplomatic entreaties and the presence of UN monitors since April.

Assad’s government, dominated by his minority Alawite sect, has denied responsibility for the killings in Qubeir, where the residents were part of the Sunni majority, and he has called the accusation a propagandist lie. But it remains unclear why the monitors were not permitted to visit the site much sooner.

‘There was a strong stench of burnt flesh in the air.’

Sausan Ghosheh UN spokeswoman

“Some homes were damaged by rockets from B.M.P.’s, grenades and a range of caliber weapons,’’ a spokeswoman for the monitors, Sausan Ghosheh, said in an e-mailed description of the visit, using the abbreviation for a Russian-made armored personnel carrier used by the Syrian military. “Inside some of the houses, the walls and floors were [splattered] with blood. Fire was still burning outside houses, and there was a strong stench of burnt flesh in the air.’’

Amid the uproar over the Qubeir killings, the fourth massacre in Syria in two weeks, multiple clashes flared in other Syrian locales Friday, including Damascus neighborhoods close to the center of the capital.

International efforts to find a way out of the Syrian crisis intensified in Washington, where Secretary of State Hillary Rodham Clinton, an outspoken opponent of Assad, met privately with Kofi Annan, the special envoy of the United Nations and Arab League. Annan, whose peace plan that placed the monitors in Syria is widely considered a failure, has insisted the plan can work if the big powers put more pressure on Assad.

Antigovernment activists first reported the Qubeir mass killings Wednesday night, which they blamed on government troops and plainclothes militia men known as shabiha. The activists said as many as 78 people, half of them women and children, had been slaughtered in the hamlet, a clutch of low-lying farmhouses with a population of 130 nestled amid cornfields about 20 miles from the city of Hama.

But Ghosheh, the spokeswoman, who accompanied the monitors, said the number and names of the victims had not been confirmed, the community was empty of residents, and “thus the observers were not able to talk to anyone who witnessed Wednesday’s horrific tragedy.’’

She said it would take time to sort out conflicting information from residents of neighboring villages. “We need to go back, cross-reference what we have heard, and check the names they say were killed, check the names they say are missing,’’ she said.

A few foreign journalists who had been permitted to travel with the monitoring team also reported evidence of multiple killings as well as evidence of attempts to hide the bloodshed. A BBC correspondent, Paul Danahar, said that neighboring villagers who approached the monitors had blamed the shabiha for the killings, and that they said the militiamen had trucked the bodies away. Another villager said sticks had been used to kill children.

“This has basically been a scorched-earth policy by whoever this was; they’ve killed the people, they’ve killed the livestock, they’ve left nothing in the village alive,’’ Danahar said in an audio recording posted on the BBC News website. He called it “an appalling scene.’’

The official Syrian account of what happened in Qubeir was starkly different. A report posted on the Syrian Arab News Agency website quoted witnesses as saying that terrorist groups, the government’s euphemism for the opposition, had attacked Qubeir with rocket launchers and machine guns, nine people had been killed, and the military and law enforcement authorities had been called in to protect the hamlet.

The report criticized unidentified “bloody satellite channels which are counterfeiting the truth to serve their interests,’’ an apparent reference to CNN, Al Jazeera, and others carrying opposition accounts of the killings.

The Friday mayhem elsewhere in Syria included clashes between troops and activists in at least one restive district of Damascus, where explosions could be heard. The Syrian Observatory for Human Rights, a British group with a network of informants in Syria, reported clashes in at least three Damascus neighborhoods, while in Homs, a center of antigovernment sentiment, the group reported “the most violent shelling’’ it had seen since the anti-Assad uprising began.

Some experts on Syria have described the Qubeir killings as part of a new stage in the Syrian conflict that has crossed dangerously into sectarianism, fomented by Assad’s government, a situation for which efforts like Annan’s peace plan are too late. “We’ve reached the point of no return,’’ said Salman Shaikh, director of the Brookings Doha Center in Qatar and a former UN official. “Diplomacy has not kept up with the reality on the ground.’’

Annan has fended off criticism that his plan cannot work and that the Syrian president has never intended to honor it.

“Some say the plan may be dead,’’ he said. “Is the problem the plan or the problem is implementation? If it’s implementation, how do we get action on that? And if it’s the plan, what other options do we have?’’