Fighting erupted in a Damascus suburb and around an army base in northern Syria on Friday, opposition sources said, as a truce marking Eid Al Adha holiday crumbled almost before it had begun.

Three people were killed by tank fire and snipers in Harasta, a town near Damascus, activists said.

The Syrian military had said it would hold fire on Friday morning following an appeal by international mediator Lakhdar Brahimi for a pause in fighting which has killed 32,000 people and which threatens to draw regional powers into the conflict.

But violations by both sides swiftly marred the truce.

Rebels in a northern town near the Turkish border said a sniper had killed one of their fighters early on Friday and a Reuters journalist there heard the sound of four tank rounds.

"We don't believe the ceasefire will work," rebel commander Basel Eissa told Reuters. "There's no Eid for us rebels on the front line. The only Eid we can celebrate will be liberation."

The Syrian Observatory for Human Rights said rebels were trying to storm the Wadi al-Daif army base, which is less than 1 km from the Damascus-Aleppo highway, and that troops had fired artillery at a nearby village.

Citing opposition activists, the British-based group also said the army had fired six rockets at the besieged Khalidiya district of Homs, wounding two people and damaging houses.

Qassem Saadeddine, head of the military council in Homs province and spokesman for the FSA joint command, said on Thursday his fighters were committed to the truce, but demanded the release of detainees by Friday morning.

Abu Moaz, spokesman for Ansar al-Islam, which includes several brigades fighting in and around Damascus, said the Islamist group doubted Assad's forces would observe the truce, though it might suspend operations if they did.

"We do not care about this truce. We are cautious. If the tanks are still there and the checkpoints are still there then what is the truce?" he asked.

Brahimi's predecessor, former UN chief Kofi Annan, declared a ceasefire in Syria on April 12, but it soon became a dead letter, along with the rest of his six-point peace plan.

Violence has intensified since then, with daily death tolls compiled by opposition monitoring groups often exceeding 200.

UN aid agencies have geared up to take advantage of any window of opportunity provided by a ceasefire to go to areas hard to access due to fighting, a UN official in Geneva said.

The UN refugee agency UNHCR said it had prepared emergency kits for distribution for up to 13,000 families - an estimated 65,000 people - in Homs and the northeastern city of Hassaka.-Reuters