BEIRUT: The UN Security Council has voted unanimously to dispatch a first team of monitors to Syria to shore up a brittle cease-fire as escalating fighting between regime and rebel forces threatened the truce at the heart of special envoy Kofi Annan's peace plan.

Syrian troops shelled residential neighborhoods and rebel gunmen fired rocket-propelled grenades in the central city of Homs on Saturday in the first use of heavy weapons since the cease-fire officially took effect Thursday. Loud booms echoed across the city as smoke rose above badly damaged apartment blocs. In other parts of Syria, both sides described several deadly shootings and ambushes, and reported at least 14 people were killed.

Saturday's resolution gave the 15-nation Security Council its first united front since the uprising against President Bashar Assad began 13 months ago — it called for immediate deployment of up to 30 monitors, to be followed by a larger contingent of up to 250 once the situation has stabilized.

Emphasizing that both sides must halt the violence that has killed more than 9,000, the council called on Syria to pull soldiers and heavy weapons out of towns and cities _ a truce provision Assad's regime has ignored. It also demanded urgent compliance with Annan's six-point plan intended to lead to talks between the regime and the opposition on Syria's political future.

The plan is widely seen as the only remaining chance for diplomacy, mainly because it has the backing of Syria allies Russia and China which shielded Assad from Security Council condemnation in the past.

Annan said in Geneva that he was ''very relieved and happy'' about the council vote. France's UN ambassador, Gerard Araud, said he hoped the vote ''will open the way to a cessation of brutal violence, and we hope that we'll be able to say to the Syrian people that the time of indiscriminate violence is finally behind it.'' The latest attacks in Homs ''lead to some doubts about the reality of the commitment of the Syrian regime,'' he added.

Western powers and opposition leaders remain skeptical about Assad's willingness to ease his tight grip on the country, ruled by his family for four decades. The regime appears to have complied with parts of the Annan plan, while flouting others.

With the exception of Homs, the military has halted random shelling and mortar attacks on rebel-held residential areas, which were the daily norm in recent weeks.

However, it has maintained an intimidating presence of troops, tanks and plainclothes security agents in the streets and demanded that anti-government protesters seek permits, despite Annan's demand that peaceful gatherings be allowed.

Since mass protests against Assad broke out in March 2011, the regime has restricted the access of outside observers, including foreign journalists to Syria. Even a small team of UN monitors could help stabilize a cease-fire by calling out those violating it.

Russia initially objected to language in a Western-backed draft of Saturday's resolution that let observers travel where they want in Syria. However, in the end Russia voted in favor.

''There have been too many casualties, too much suffering ... with too many destructive consequences if the crisis continues to ratchet up,'' not only for Syria but for the region, explained Russia's UN ambassador, Vitaly Churkin.

Annan spokesman Ahmad Fawzi has said an advance team of about a dozen observers was on standby to fly to Syria once the Security Council approved the mission and could quickly be increased to 30.

The council said it wants to dispatch a larger UN team after talks between UN Secretary-General Ban Ki-moon and the Syrian government, and once all violence has halted. Ban said Saturday that he will make concrete proposals by Wednesday for a larger UN team that could include about 250 observers.

The heaviest fighting erupted Saturday in Homs, an opposition stronghold pounded by daily regime shelling in the three weeks leading up to the cease-fire. The Britain-based Syrian Observatory for Human Rights, an activist group, said at least three civilians were killed by tank shells and mortar rounds Saturday.