Dozens of civilians in Syria's city of Homs were killed in cold blood, the government and opposition said, disputing responsibility for what both sides called a massacre.

State media in Damascus, which often ignores activists' claims, confirmed killings in Homs on Monday but blamed "armed terrorists" as it frequently calls those behind the uprising.

The Britain-based Syrian Observatory for Human Rights said at least 16 people were killed Sunday night in Homs, while the Local Co-ordination Committees said 45 were killed. Both groups said children were among the dead.

The carnage in Homs followed the army's launch of an assault on Idlib city in the northwest and coincided with the first visit to Syria by UN-Arab League envoy Annan, who was seeking agreement on a ceasefire, humanitarian access and political dialogue.

According to Al Jazeera's Anita McNaught, government forces are pressing on with new offensives in other parts of central and northern Syria.

Reporting from Idlib, McNaught described the bombing as "earth-shaking and relentless."

She compared the battle for Idlib with the fight for the Libyan city of Benghazi, the opposition stronghold played a key role in the uprising against the late Muammar Gaddafi.

"What we saw in Idlib was a re-run of something like Benghazi, though the ending is unlikely to be like the ending Benghazi had. The Syrian government won't let that happen," McNaught said.

'Collective punishment'

The reports of the killings in Homs add to concerns that the hundreds of civilian deaths caused by the fighting will be compounded by reprisals against opposition supporters in the recaptured towns and neighborhoods.

Activists in Homs and Syrian TV showed videos of 16 bloodied bodies, their hands tied behind their backs, lying on
trash-littered streets and in blood spattered rooms.

Opposition groups also uploaded videos of corpses being wrapped in white shrouds as crowds lined up to pray for the dead, who are believed to have been killed late on Sunday.

A medical worker in Homs working in the rebel-held neighborhood of Khalidiya said many of the victims were killed
with knives and some of the women appeared to have been raped.

"We received the bodies in two batches ... we tried to go to see if there were any survivors but they were all dead," said the medical worker, who called himself Yazan.

The government and opposition each said the other side was to blame for the killings in Homs, where Syrian forces retook a rebel-held district on March 1 after a 26-day siege.

United Nations investigators on Monday said Syria subjected civilians to "collective punishment" and that its forces stand accused of carrying out executions and mass arrests in Bab Amr.

"The terrorist armed groups have kidnapped scores of civilians in Homs, killed and mutilated their corpses and filmed them to be shown by media outlets," Syria's state news agency said.

Opposition activists said on Monday that 25 civilians were killed in the attack on Idlib.

In a phone interview with Al Jazeera, Abu Hani, a city resident, described the conditions in local hospitals as shocking.

"After shelling the city, security forces began a house-to-house search for activists and protesters," he said. "And soldiers have been granted complete freedom to loot everything from homes and shops."

Also Monday, state news agency SANA reported that an "armed terrorist group'' blew up a pipeline that transports diesel from the central province of Homs to the nearby region of Hama, setting it on fire.

There have been several fires and explosions cutting oil and gas pipelines since the uprising began. Damascus blames them on armed groups but the opposition says they are caused by government shelling.

In the northeastern city of Qamishli, thousands of Kurds marched to mark the eighth anniversary of clashes between Syrian Kurds and security forces.

The UK-based observatory said security forces opened fire at the demonstration, wounding at least three people.

The ongoing violence comes after two days of talks between Syrian President Bashar al-Assad and Kofi Annan, the joint envoy of the Arab League and UN to Syria.

PHOTO CAPTION

Smoke rises as Idlib city is shelled by government forces March 11, 2012.

Aljazeera