BEIRUT >> U.N. observers on Friday could still smell the stench of burned corpses and saw body parts scattered around a Syrian farming hamlet where nearly 80 men, women and children were reported slain this week. The scene held evidence of a “horrific crime,” a U.N. spokeswoman said.

The observers were finally able to get inside the deserted village of Mazraat al-Qubair after being blocked by government troops and residents, and coming under small arms fire Thursday, a day after the slayings were first reported.

In central Damascus, rebels brazenly battled government security forces in the heart of the capital Friday for the first time, witnesses said, and explosions echoed for hours. Government artillery repeatedly pounded the central city of Homs and troops tried to storm it from three sides.

U.S. Secretary of State Hillary Rodham Clinton met with international envoy Kofi Annan in Washington to discuss how to salvage his faltering plan to end 15 months of bloodshed in Syria. Western nations blame President Bashar Assad for the violent crackdown on anti-government protests that grew out of the Arab Spring.

The U.N. team was the first independent group to arrive in Mazraat al-Qubair, a village of about 160 people in central Hama province. Opposition activists and Syrian government officials blamed each other for the killings and differed about the number of dead.

Activists said that up to 78 people, including women and children, were shot, hacked and burned to death, saying pro-government militiamen known as “shabiha” were responsible. A government statement on the state-run news agency SANA said “an armed terrorist group” killed nine women and children before Hama authorities were called and killed the attackers.

Sausan Ghosheh, spokeswoman for the U.N. observers, said residents’ accounts of the mass killing were “conflicting,” and that they needed to cross check the names of the missing and dead with those supplied by nearby villagers. Mazraat al-Qubair itself was “empty of the local inhabitants,” she said.

“You can smell the burnt smell of the dead bodies,” Ghosheh said. “You could also see body parts in and around the village.”

Ghosheh said she saw two homes damaged by shells and bullets. She spoke of burned bodies found in a house, but did not elaborate and was not clear whether the U.N. team saw them.

She told the BBC: “We can say that there was definitely a horrific crime that was committed. The scale is still not clear to me.”

A BBC correspondent traveling with the U.N. observers described the hamlet as an “appalling scene” of burned-out houses and gore.

“There are pieces of human flesh lying around the room, there is a big pile of congealed blood in the corner, there’s a tablecloth that still has the pieces of someone’s brain attached to the side of it,” said the correspondent, Paul Danahar.

“They killed the people, they killed the livestock, they left nothing in the village alive,” he added.

The U.N. observers also visited a cemetery where some of the dead were buried, according to an activist in Mazraat al-Qubair.

Activists said the Sunni hamlet is surrounded by Alawite villages. Alawites are an offshoot of Shiite Islam and Assad is a member of the sect, while the opposition is dominated by Sunnis.

The United States condemned Assad over the killings, saying he has “doubled down on his brutality and duplicity.”

The violence followed another mass killing last month in a string of villages known as Houla, where 100 people including many women and children were also shot and stabbed to death. The opposition and the regime blamed each other for the Houla massacre.

In April, the U.N. said more than 9,000 people have been killed since the crisis began in March 2011, but it has been unable to update its estimate since and the daily bloodshed has continued in past weeks. Activists put the number of dead at about 13,000.

Before her meeting with Annan, Clinton said they would look at “how to engender greater response by the government of Syria to the six-point plan that he has put forth.”

Annan’s plan calls for an end to violence followed by a political transition. Although Assad agreed to it, the violence has continued unabated with reports of brutal massacres against innocents.

Annan allowed that some people “say the plan is definitely dead.” He asked rhetorically whether the problem is the plan or its implementation.

“If it’s implementation, how do we get action on that?  And if it’s the plan, what other options do we have?” he said.

U.N. diplomats say Annan is proposing that world powers and key regional players, including Iran, come up with a new strategy to end the conflict.

In Damascus, government troops clashed with defectors from the Free Syrian Army in the Kfar Souseh district in some of the worst fighting yet in the capital. The clashes were a clear sign that the ragtag rebel group has succeeded in taking its fight into the regime’s base of power.

“I’ve been hearing shooting and explosions for hours now and can see smoke rising from the area,” a witness who spoke on condition of anonymity for security concerns told The Associated Press.

On Thursday night, armed rebels took part in a large anti-government rally in the same district, witnesses said, in a rare and bold public appearance by the fighters in the capital. Friday’s fighting began when the rebels attacked a government checkpoint in the morning, according to Rami Abdul-Rahman of the Britain-based Syrian Observatory for Human Rights.

“The men are shouting ‘God is great,’ women are crying,” said Omar, a Damascus resident who would not provide his family name for fear of reprisal by Syrian officials. The sound of machine gun fire and blasts could be heard in the background as he spoke by Skype.

A resident of the Damascus neighborhood of Qaboun said the battles began in his area after Syrian forces opened fire on an evening demonstration, killing a young man he identified as Mahmoud Said. Following that, gunmen hiding in the area began clashing with security forces. Nobody was sure how many people were killed, because they could not leave their houses, said the resident, who asked not to be identified because he feared government reprisal.

The Observatory and another activist group, the Local Coordination Committees, said clashes also broke out in other Damascus districts. There was no immediate word on civilian casualties but the LCC said three rebels were killed.

In Homs, one of the main battlegrounds of the uprising, the offensive against Khaldiyeh appeared to be a new push by regime forces to retake the enclave that has been held by rebels for months.

Pro-Assad troops overran the opposition-held neighborhood of Baba Amr on March 1 after a government siege killed hundreds of people — many of them civilians — in Syria’s third-largest city.

Activist Tarek Badrakhan said regime troops were trying to advance on Khaldiyeh from three sides, battling with rebels trying to stop them.

“This is the worst shelling we’ve had since the start of the revolution,” he said via Skype. A shell could be heard exploding in the background as he spoke.

Shells were hitting the neighborhood at a rate of five to 10 a minute, said a statement by the Observatory.

There was no immediate word on casualties from Khaldiyeh, whose original 80,000 inhabitants have mostly fled.

Amateur videos showed missiles exploding into balls of flames in the crowded concrete jumble of homes, with thundering crashes that sent up plumes of heavy gray smoke. The videos suggested the attack began at dawn as birds chirped and roosters crowed. In one video, the missiles came in rapid succession, four exploding in less than a minute.

Homs has been one of the hardest-hit regions in Syria since the uprising began.

The government news agency reported troops on the eastern Lebanese border area clashed with rebels, who they said were trying to smuggle in three pick-up trucks full of weapons. The agency said they destroyed one car, but two sped back into Lebanon

In several locations across Syria on Friday, troops fired tear gas and live ammunition in an attempt to disperse thousands of anti-government protesters, activists said, including the northern provinces of Idlib and Aleppo, the southern region of Daraa and in the suburbs of Damascus. Several people were reported killed, but the numbers were not immediately clear.

In Geneva, International Committee of the Red Cross spokesman Hicham Hassan said Syria’s humanitarian situation was worsening. And Kristalina Georgieva, European commissioner for humanitarian aid, said in Brussels that there are 1 million “vulnerable people who need humanitarian assistance.”

“Between 200,000 and 400,000 are internally displaced … and we have 95,000 refugees in Turkey, Lebanon and Jordan primarily,” she said.

Also on Friday, the Committee to Protect Journalists said five citizen journalists documenting the unrest in Syria were killed in a two-day period at the end of May.