He said an aerial assault on Sunday, which hit an open-air market in the village of Azaz, near the Turkish border, left at least 20 people dead and wounded 99. The strike came as many people from around the region were shopping. “A sunny day,” he said. “Many children were out with their parents.”

Other signs that children had died in government bomb strikes were seen in videos uploaded on the Internet, although they could not be independently corroborated. In one, a boy’s naked body, thickly coated in gray dust, lay prone amid rubble, in footage that activists said was shot on Monday in Moadamiyeh, a suburb southwest of the capital, Damascus, on a street echoing with high-pitched wails and crammed with cinder blocks from collapsed facades. In a room exposed by the blast, a woman could briefly be seen carrying the motionless body of a child.

A second video showed the bodies of half a dozen children laid out on blood-soaked blankets, including one curly-headed toddler no more than 2 years old. “Let the whole world observe, those are the victims,” a narrator said on the video. “Those are the ones Bashar al-Assad is fighting.”

The official SANA news service said the Moadamiyeh explosion was caused by an insurgent mortar attack, not by government warplanes. It also said that airstrikes had killed scores of rebels around the country, including many it identified by name.

The tally of children killed in airstrikes, according to activists, included seven children killed while playing outside in Hizza, east of Damascus, according to video that showed women weeping over their body parts; three in the northern city of Aleppo; two in an Aleppo suburb; four in Latamna, in Hama Province.