Syrian regime forces have "massacred" more than 90 people, including 25 children, in the town of Houla, the Syrian Observatory for Human Rights said on Saturday.
Deadly shelling on Friday continued late into the night, the Observatory's Rami Abdel Rahman told AFP.
"Many people are fleeing Taldau village in Houla," the Observatory said, adding that residents feared new attacks on the town, in the central province of Homs.
Regime forces pounded the edges of Houla on Friday, Abdel Rahman said, adding that this caused residents of the town's outskirts to flee towards the centre.
Amateur videos posted on YouTube showed horrifying images of children lying dead on the floor, with some of their corpses badly mangled. At least one child had had part of his head blown off.
The Britain-based watchdog condemned the Arab and international communities, describing them as "complicit with the Syrian regime in the Houla massacre."
The international community was "silent in the face of the massacres committed by the Syrian regime," it said.
Earlier, the opposition Syrian National Council urged the UN Security Council to act after regime forces "massacred" what it said was more than 110 people in 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.