At least 12 people were killed in air strikes on the rebel-held western Syrian town of Rastan on Wednesday, a local doctor and a monitoring group said, despite a government-declared nationwide temporary truce.
The British-based monitoring group, the Syrian Observatory for Human Rights, also said another 12 people were killed in rebel-controlled Ariha, north of Rastan, including three children.
Pictures from Ariha showed "White Helmet" rescue workers lifting slabs of broken grey concrete as they searched for survivors in the crumbled wreckage of a building.
Syrian government forces, backed by Russia's air force and President Bashar al-Assad's regional allies, said this week they had extended a nationwide "regime of calm" until just before midnight on Thursday.
But fighting has continued on several fronts.
The doctor in Rastan, about 100 miles (160 km) north of Damascus, said 12 people had been killed in the air strikes and the death toll was likely to rise because many others were seriously wounded. The Observatory put the death toll at 16.
Rastan is part of a rebel-held pocket of territory surrounded by government forces. Ariha, further north, is in the rebel-controlled province of Idlib, bordering Turkey.
The air strikes came as pro-government forces fought rebels and Islamist factions in the northern city of Aleppo.
The rebel half of the city has been effectively cut off for nearly a week after government forces backed by allies including Lebanon's Hezbollah advanced to within a few hundred meters (yards) of the only road into the rebel districts.