The opposition Syrian National Council has urged the UN Security Council to act urgently after claiming that regime forces "massacred" scores of civilians, including many children, in the town of Houla.

The latest flare-up of violence came as Kofi Annan, the UN-Arab League envoy to Syria who brokered a repeatedly violated ceasefire last month, finalised plans to return to Damascus.

The Britain-based Observatory said the shelling had killed more than 90 people in Houla, including 25 children.

Amateur videos posted on YouTube showed horrifying images of children lying dead on a floor. Some of their corpses badly mangled, including at least one child whose head had been partly blown away.

The Observatory accused the international community of standing “silent in the face of the massacres committed by the Syrian regime.”

Earlier on Saturday, SNC spokeswoman Basma Kodmani said “more than 110 people were killed (half of whom are children) by the Syrian regime’s forces” in Houla. “Some of the victims were hit by heavy artillery while others, entire families, were massacred.”

A report by UN Secretary General Ban Ki-moon said groups fighting President Bashar Al Assad now control “significant” parts of some cities and there is “considerable physical destruction” across the country.

The report is to be debated by the Security Council next week.