BEIRUT — The U.N. Security Council voted unanimously Saturday to dispatch a team of monitors to Syria to shore up a 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 in the first use of heavy weapons since the cease-fire officially took effect Thursday. Explosions echoed across the city as smoke rose above badly damaged apartment blocks. 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.

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 compliance with Annan’s six-point plan intended to lead to talks between the regime and the opposition.

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.

France’s U.N. 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.”