BEIRUT/GENEVA - Damascus residents reported artillery barrages by Syrian troops hours before Friday's scheduled start of a ceasefire to mark the Muslim holiday of Id al-Adha.They said that on Thursday night troops stationed on a mountain overlooking the Syrian capital targeted Hajar al-Aswad, a poor neighborhood inhabited by refugees from the Golan Heights. There were no immediate reports of casualties."Consecutive artillery volleys from Qasioun shook my home," said Omar, an engineer who lives in al-Muhajereen district on a foothill of the mountain.On Thursday a Free Syrian Army commander gave qualified backing to the truce, proposed by UN-Arab League envoy Lakhdar Brahimi, but he demanded that Syrian President Bashar Assad free detainees. An Islamist group said it was not committed to the truce, but may halt operations if the army did.Brahimi proposed the temporary truce to stem, however briefly, the bloodshed in a conflict which erupted as popular protests in March last year and has escalated into a civil war which activists say has killed more than 32,000 people.The fighting pits mainly Sunni Muslim rebels against Assad, from the Alawite faith which is linked to Shi'ite Islam, and threatens to draw in regional Sunni Muslim and Shi'ite powers and engulf the whole Middle East, Brahimi has warned."On the occasion of the blessed Id al-Adha, the general command of the army and armed forces announces a halt to military operations on the territory of the Syrian Arab Republic, from Friday morning ... until Monday," an army statement read on state television said.It reserved the right to respond if "the armed terrorist groups open fire on civilians and government forces, attack public and private properties, or use car bombs and explosives."It would also respond to any reinforcement or re-supplying of rebel units, or smuggling of fighters from neighboring countries "in violation of their international commitments to combat terrorism".Qassem Saadeddine, head of the military council in Homs province and spokesman for the FSA joint command, said his fighters were committed to the truce. "But we not allow the regime to reinforce its posts. We demand the release of the detainees, the regime should release them by tomorrow morning," he said.Abu Moaz, spokesman for Ansar al-Islam, 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 said of the organization, which includes several brigades fighting in the capital and Damascus province.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.