As Annan flies out, Assad's men go in to kill the innocent

There were renewed fears that Syria was slipping towards all-out civil war last night after opposition activists claimed that scores of men, women and children had been butchered by regime militias roaming through a rebel neighbourhood in Homs – just 24 hours after the former United Nations chief Kofi Annan jetted out of Damascus saying he had drawn up a plan for ending the crisis.

Reports emerging from the shell-blitzed city suggested entire families had been shot or had their throats slit, with numerous videos being uploaded to YouTube showing blood-soaked corpses in homes and backyards.

"Sunni people in Homs are talking about declaring holy war," an activist calling himself Abo Emad said. He added that alleged massacres by Shia Alawi paramilitaries loyal to President Bashar al-Assad were radicalising communities in Homs, an area that has been plagued by sectarian kidnappings and murders in recent months. Many analysts fear the violence in the city could lead to wider civil strife.

State media confirmed that mass killings had taken place, but blamed the deaths on "terrorists" fighting against the government. But the Local Co-ordination Committees of Syria, a network of activists which works to publicise the uprising, said 45 people had been murdered by loyalist militias in Karm Zeitoun, a mixed Alawi-Shia neighbourhood, which was controlled by rebel troops until last month.

A number of videos have since appeared on the internet purporting to show victims of the massacre. One showed the blood-stained bodies of at least a dozen middle-aged men.

Rami Abdul-Rahman, from the British-based Syrian Observatory for Human Rights (SOHR), said more than 100 bodies had been delivered to hospitals in Homs over the past three days. It was still unclear who was responsible for the killings, he said. According to Abo Emad, mothers and young girls were raped by gangs of paramilitaries as they went house-to-house in the neighbourhood. "If the regime is saying it was the opposition doing this, then they can go to hell," he said. "How could we kill our own children?"

The latest outbreak of violence comes after a week of intensive diplomatic efforts, which appear to have come to nothing. Despite holding two rounds of talks with the Syrian President, Mr Annan failed to secure ceasefire talks between the government and rebel groups. And the violence shows no sign of slowing: as well as the apparent massacre in Homs, a car bomb exploded in the city of Deraa, killing three people.

Talks moved on to the UN Security Council yesterday, where again there were harsh words for the Assad regime. The "horrific campaign of violence" had "shocked the conscience of the world", Hillary Clinton, the United States' Secretary of State, said. The British Foreign Secretary, William Hague, again attacked Damascus, which has "failed to fulfil its responsibility to protect its own people". Their comments came after Valerie Amos, the UN's humanitarian chief who visited Homs last week, said she was, "horrified by the destruction," she saw.

Any formal censure from the UN is unlikely given veto-holding Russia and China, who insist that all sides commit to a peaceful solution.