Civilians caught in the cross-fire were among the 13 people killed in the fighting on Saturday, according to residents.

Fighters from the Jabal Mohsen district, home to the minority Shiite Alawite sect to which Syrian President Bashar al-Assad belongs, have been involved in several skirmishes in recent weeks with opposition supporters from the Sunni Muslim area of Bab al-Tabbani.

A woman and her son were among those killed in the Bab al-Tabanni district, apparently by rocket fire.

Long-standing disputes between the neighborhoods already exist, but the conflict in Syria has led to increasing strife between them.

Sporadic gun fire and the sound of rockets were heard from midnight onwards, with some residents forced to flee their homes. The army and police were later deployed in the area.

The split represents a wider division in Lebanese society, with the ruling coalition led by Hezbollah supporting the Assad administration and the opposition backing the uprising.

Speaking at the opening of an Arab League meeting in Qatar, the UN and Arab League's Syria envoy Kofi Annan expressed fears about violence within Syria spilling over into neighboring countries.

'Worrying sectarian dimension'

Annan also warned of the prospect of an "all-out war with a worrying sectarian dimension" in Syria.

"The situation is complex and it takes everyone involved in the conflict to act responsibly if the violence is to stop. But the first responsibility lies in the Syrian government and President Assad," he said.

The Arab League's ministerial committee on Syria called on Annan to set out a deadline for his six-point peace plan to be accepted.

"We request Mr Annan to set a time frame for his mission because it is unacceptable that massacres and bloodshed continue while the mission is ongoing indefinitely," said Qatari Prime Minister Sheikh Hamad bin Jassim Al-Thani.

The committee called on the UN to refer the Annan plan to "Chapter VII," meaning that the council would spell out the possible actions it would take against Damascus.

rc/ncy ( AFP, Reuters)