Dozens of civilians in the formerly besieged Syrian city of Homs have been massacred in cold blood, according to state media and the opposition movement.

Both sides in Syria's bitter armed conflict have blamed each other is responsible for the killing of women and children in Homs and other cities, after footage emerged of blood-soaked and mutilated bodies over the weekend.

The accusations come as United Nations/Arab League peace envoy Kofi Annan left Damascus on Sunday without finalizing a ceasefire agreement nor establishing a way to provide humanitarian access to trapped civilians.

The terrorist armed groups have kidnapped scores of civilians in the city of Homs, central Syria, killed, and mutilated their corpses and filmed them to be shown by media outlets, state news agency SANA said on its website, Reuters reported.

According to activists from the Local Coordination Committees of Syria, at least 45 women and children have been stabbed and burned in the Homs district of Karm al-Zeitoun, while several others were slain near the city's former rebel bastion of Babr Amr in Jobar.

Several groups have blamed Alawite shabbiha militias loyal to President Bashar al-Assad for the killings, saying the groups were under the protection of Syrian government forces, Reuters said.

Activist Waleed Fares said that 30 to 40 tanks had arrived in Karm al-Zeitoun on Sunday night.

We know now that four families have been killed by shabbiha. We have 21 names and we are trying to confirm the names of the rest, he told Reuters via Skype.

The victims, he added, were all from Syria's Sunni Muslim majority.

It's quiet now but I have been hearing gunfire all night.

The Free Syrian army helped move the bodies to one place. Otherwise the regime forces would have hidden the evidence, he said.

Elsewhere, a car bomb exploded outside a girls' school in the southern city of Deraa killing a school girl and wounding 25 others.

Activists said members of the school had taken part in anti-Assad demonstrations.