At least three civilians were killed by gunfire and heavy machinegun fire in the Baba Amro neighbourhood of Homs," said the Syrian Observatory for Human Rights.

"The sound of explosions was also heard in the area of Karm al-Zaitun" in the flashpoint central city, it said.

In the northwestern province of Idlib, near the border with Turkey, "four (Shabiha) militiamen loyal to the regime were killed by suspected deserters in the town of Saraqeb," added the Britain-based Observatory.

On Friday, Syrian troops killed at least 23 people when demonstrators took to the streets denouncing "despots and tyrants," as world powers cast doubt on the regime's commitment to a peace deal agreed with the Arab League.

The plan calls for an end to violence, the release of those detained, the withdrawal of the army from urban areas and free movement for observers and the media, as well as talks between the regime and opposition.

Members of the UN Human Rights Council said they seek to "shine a spotlight" on violations in Syria as a UN commission of inquiry prepared to file later this month a report on the violence-wracked country.