Reports of dozens killed in heavy shelling as Russian foreign minister heads to Damascus to push for reforms.
A Syrian military assault on Homs has killed dozens of people, as world powers scramble for a diplomatic strategy to end the violence in the country after the defeat of a UN Security Council resolution.
Russia's foreign minister Sergei Lavrov is due to visit Damascus on Tuesday to press President Bashar al-Assad to implement democratic reforms after Russia and China vetoed any UN-backed measures against the Syrian government over its crackdown on the 11-month uprising.
Ahead of his visit, Lavrov said condemnation of Moscow's veto had verged on "hysteria"
He said Moscow sought "the swiftest stabilisation of the situation in Syria on the basis of the swiftest implementation of democratic reforms whose time has come".
The Russian initiative comes a day after the United States shut its embassy in Damascus and Belgium and Britain recalled their ambassadors.
US President Barack Obam said that while the West was prepared to lean hard on President Bashar al-Assad diplomatically, they still had no intention of using force to topple him.
"I think it is very important for us to try to resolve this without recourse to outside military intervention. And I think that's possible," Barack Obama told NBC's Today show.
Activists and witnesses said the Syrian army had stepped up its attacks on opposition fighters after the UN resolution was blocked by Russia and China.
Abu Abdo Alhomsy, an activist of a revolutionary council in Homs, described to Al Jazeera an attack on Monday on the city as live pictures showed smoke billowing into the sky.
'Rockets are falling'
"It is horrible right here," Alhomsy said. "Rockets are falling. There are massive explosions that shook buildings. We don't know really what to do.
"Its a massive attack - a new massacre is happening here. Nobody can go out, we don't know how many homes have been hit or how many people died."
The UK-based opposition group, the Syrian Observatory for Human Rights (SOHR), said at least 29 civilians were killed and dozens more wounded.
But it said the death toll was likely to rise because many of the wounded had suffered critical injuries.
Syrian authorities, who have denied firing on houses, said security forces killed "tens of terrorists" in Homs on Monday morning. An interior ministry statement said six members of the security forces were killed in the clashes.
The shelling, which began at dawn, was mainly targeting the neighbourhoods of Khaldiyeh, Bab Amr, Inshaat and Bab Sbaa, the SOHR said.
Video received by Al Jazeera from opposition activists on Sunday showed the apparent devastation caused by a military offensive in the Bab Amr neighbourhood of Homs.
A video posted by activists on YouTube apparently showed a field hospital hit by the shelling in Bab Amr. Wounded patients could be seen lying on stretchers on the floor amid pools of blood and shattered glass. Bodies of dead people with horrific injuries were also shown inside the hospital.
The authenticity of the video could not immediately be verified.
Syrian state television has accused "armed gangs" of being behind the latest violence in Homs.
Activists and witnesses said the army had been shelling Bab Amr "indiscriminately" since Sunday morning.
The video images appear to show people who have been shot and hit by shrapnel, including heavily injured young children.
Speaking to Al Jazeera, Danny Abdul Dayem, a resident of Homs, said: "It has been terrible. There is non-stop bombing with rockets, mortar bombs and tank shells. There were more than 50 people injured in Bab Amr today.
"I saw with my own eyes kids with no legs, and a kid who lost his whole bottom jaw. It is terrible."
In the northeast of the country, army deserters destroyed a military control post early on Monday, killing three officers and capturing 19 soldiers in the process, the SOHR said.
The fighting happened in the village of Al Bara in the Idlib region, it said.
It said none of the army deserters involved was killed and that the regular army post was completely destroyed.
The death toll in Syria rose to at least 88 people over the weekend - one of the bloodiest since the uprising against Bashar al-Assad's government erupted almost 11 months ago.
Opposition groups say at least 6,000 people have now been killed in Syria.
Source:Al Jazeera and agencies