The carnage in Homs, as well as a military assault on the northwestern city of Idlib, coincided with a weekend peace mission by UN-Arab League envoy Kofi Annan, who left Damascus on Sunday without agreement on a truce or humanitarian access.
"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.
Footage posted by opposition activists on YouTube showed men, women and children lying dead in a blood-drenched room.
The Local Coordination Committees of Syria, a network of opposition activists, said at least 45 women and children had been stabbed and burned in the Homs district of Karm al-Zeitoun.
It said another seven people were slain in the city's Jobar district, which adjoins the former rebel bastion of Baba Amr.
Activists contacted in Homs accused Alawite militiamen loyal to President Bashar al-Assad of carrying out the killings under the protection of regular Syrian military forces.
Syrian government restrictions make it difficult to assess conflicting reports by the authorities and their opponents since a popular uprising against Assad began a year ago.
SANA said the Homs killings "perpetrated by the armed terrorist groups and aired by (satellite TV channels) Al Jazeera and Arabiya ... coincide with today's UN Security Council session to call for foreign interference in Syria".
UN meets on Arab revolts
The Security Council holds a special meeting on Arab revolts later on Monday and U.S. Secretary of State Hillary Clinton will meet Russian Foreign Minister Sergei Lavrov on the sidelines.
Russia and China have blocked attempts to pass a Security Council resolution condemning Damascus for its attempts to crush the rebellion, in which the United Nations says well over 7,500 people have been killed. Syrian authorities said in December insurgents had killed over 2,000 soldiers and police.
The United States has drafted a new resolution, but Washington and Paris say they doubt it will be accepted.
China sounded an optimistic note, but gave no details.
"China has actively participated in discussion about this draft resolution, and raised its ideas about revising it," Foreign Ministry spokesman Liu Weimin said on Monday.
"We also support the international community playing an active role in a political solution to the Syria issue."
China and Russia, as well as Western and Arab nations, have voiced support for Annan's peace mission, but no common ground has emerged between Assad, who is bent on crushing dissent, and his opponents, who are determined to overthrow him.
"The situation is so bad and so dangerous that all of us cannot afford to fail," Annan said in Damascus on Sunday.
Moscow and Beijing want any international blame for the violence to be apportioned evenly and say both sides should be encouraged to stop fighting. Saudi Arabia and Qatar have taken a hawkish line, calling for the rebels to be armed.
"The regime in Syria is committing a massacre of its own citizens," Saudi Foreign Minister Saud al-Faisal said on Sunday after talks with his German counterpart Guido Westerwelle.
Westerwelle said in Riyadh: "We cannot accept the completely unreasonable continuation of the atrocities being perpetrated by the Assad regime against its own people."
Western and Arab countries have sought to isolate Assad, but he has a few allies, notably Iran, which has invited Iraq, Lebanon and Syria to a conference in Tehran on March 18 to "support the Syrian regime against its opponents", the pan-Arab Al Hayat newspaper reported on Monday.
Citing ministerial sources, it said "official Lebanon" had declined the invitation. Lebanon, deeply split over the crisis in its powerful neighbour, has sought to avoid taking sides.