The Britain-based Syrian Observatory for Human Rights said the bombing in the village of Ziyara in the central province of Hama was carried out by Jabhat al-Nusra, an Islamist group. Activists from the area reported that the operation was in coordination with other armed rebel groups.

The attack was one of the deadliest on pro-regime forces since the start of the revolt against President Bashar al-Assadin March last year.

The observatory also reported that more than 20 rebel fighters were killed by a fighter jet air-strike on the town of Harem in the northern province of Idlib. A rebel leader in the town was also seriously injured and is thought to be dead.

State-run TV SANA and the Britain-based Observatory said a car bomb attack had also killed 11 people and wounded dozens in the west Damascus district of Mazzeh.

The rebels have scored significant gains in recent weeks and now hold swathes of territory in the country’s north, but have struggled to gain ground in and around Damascus and in the commercial hub Aleppo amid heavy bombardment from government air power, according to AFP.

The escalating conflict has added importance to a meeting of the Syrian National Council in Qatar, where Washington is pushing for an overhaul of the opposition as U.S. officials have expressed disappointment with the SNC’s inability to create a consistent plan and its lack of agreement and cooperation with different internal groups.

Syrian opposition factions were at odds Monday in talks seeking to forge unity Washington says is needed to oust the Assad regime.

The Syrian National Council, the main exiled opposition coalition, based Turkey, disagreed with a U.S.-backed proposal to set up a larger umbrella group the BBC reported.

The new group, proposed by well-known exiled dissident Riad Seif, would include representation of rebel fighters, opposition military councils and minority groups.