Fierce gunfights between security forces and rebels have broken out on the streets of a neighbourhood in the Syrian capital, Damascus, residents said, as government troops battled to take back the rebel bastion of Khaldiyeh in the central city of Homs.
Residents of Damascus' Mezze district said they were hiding in their homes on Friday as gunfire crackled outside.
"The gunfire is so loud; I think some bullets could have hit the house. I'm afraid to go outside to see what is happening," one resident said.
Activists and Syrian state television said a car bomb exploded in the Qadsiya suburb of Damascus, killing at least two members of the security forces.
Syrian TV blamed the bomb on "terrorists," using the term it frequently uses to describe rebels fighting forces loyal to President Bashar al-Assad.
In the early stages of the 15-month-old uprising, Damascus remained firmly under government control as Assad's forces tried to crush opposition in other parts of the country.
But in recent months shooting and bombings have erupted in several neighbourhoods.
'Scattered body parts'
UN monitors on Friday finally reached the village of Mazraat al-Qubeyr in Hama province, where activists say 78 people were reported massacred two days ago.
The smell of burnt flesh hung in the air and body parts lay scattered around the deserted village, a UN monitor told journalists after visiting the site.
According to preliminary evidence, troops had surrounded al-Qubeyr and pro-government gangs entered the village and killed civilians with "barbarity," UN chief Ban Ki-moon told the UN Security Council.
Damascus has denied responsibility, blaming the killings on foreign-backed "terrorists".
Meanwhile, a video has emerged of Syrian soldiers apparently abusing the bodies of dead opposition activists in Idlib near the Turkish border.
The gruesome footage, recorded in March but only posted online on Friday, showed what appeared to be Syrian soldiers kicking and stepping on bodies. The victims were said to be volunteers who moved wounded people across the border into Turkey.
The pictures were taken by one of the soldiers and leaked to the opposition, activists said.
In fresh violence on Friday, troops battled to take back the rebel bastion of Khaldiyeh in the central city of Homs, bombarding it "at a rate of five shells a minute," the UK-based Syrian Observatory For Human Rights said.
Elsewhere, an explosion in front of a police station in the northwestern city of Idlib killed five people, including two security forces members, the activist group said.
In all, more than 20 people were reported killed on Friday, including two members of the security forces who died in a blast in the Damascus suburb of Qadsiya, the observatory said.
In Kfar Zita, a town in the province of Hama, people emerged from mosques to demonstrate chanting: "We don't want peaceful (revolt). We have bullets and Kalashnikovs!"
More than 13,500 people have been killed in the crackdown on dissent that followed the eruption in mid-March 2011 of anti-government protests and the increasingly violent insurgency against Assad's government, the Observatory said.
UN-Arab League envoy Annan said in Washington that he would discuss with US Secretary of State Hillary Clinton "how we can put additional pressure on the government and the parties to get the plan implemented."
Annan said "everyone is looking for a solution" but acknowledged doubts about a peace deal he brokered, which calls for a ceasefire and dialogue to end more than a year of violence aimed at toppling President Assad.
"Some say the plan may be dead. Is the problem the plan or the problem is implementation? If it's implementation, how do we get back on track? And if it is the plan, what other options do we have," he asked.
In-depth coverage of escalating violence across Syria
In Moscow, Clinton's point man on Syria, Fred Hof, met Russian diplomats in a bid to persuade Russia to back Assad's removal.
But Mikhail Bogdanov, the Russian deputy foreign minister said after the meeting that Moscow had no information about a leadership change being planned in Damascus and pointedly failed to make any public call for one.
"I do not know anything about such plans by the Syrian president," Bogdanov told state news agency RIA Novosti.
In other developments, the Red Cross said the situation was "extremely tense" in many parts of Syria and that it was attempting to deliver humanitarian aid to 1.5 million people directly or indirectly affected by the bloodshed.