Russian warplanes carried out a "massacre" at Injara in north-west Aleppo where they hit three schools with air strikes killing 35 children and injuring dozens, Syria's opposition co-ordinator Riad Hijab said on Monday.
Syrian Observatory for Human Rights (SOHR) had earlier reported at least 15 people, 12 of whom were children, were killed and at least 25 others, all of them children and teachers, were injured by a Russian air strike on a school in town of Anjara of Syria's Aleppo Province,
The group said there had been heavy air strikes and clashes between government and rebel forces since Sunday in the northern province, which is controlled by a mixture of opposition fighters.
The Britain-based monitor also reported that three children were killed by rebel rocket fire on a government-held district in Aleppo city.
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Control of the city has been divided between government forces in the west and rebel fighters in the east since shortly after fighting began there in mid-2012.
Regime forces regularly carry out air raids on the east, while rebels fire rockets into the west.
The situation is largely reversed in the countryside surrounding the city, with rebels controlling much of the area west of Aleppo, and the regime present to the east.
Russia, a staunch ally of Bashar al Assad's regime, began air strikes in support of the Syrian regime in late September.
It says it is targeting DAESH positions, but a third of those killed in its strikes have been civilians, according to the Observatory.
The monitor said in late December that Russian air strikes had killed more than 2,300 people since they began on September 30, among them 792 civilians.
Moscow has slammed as "absurd" allegations that its strikes have killed civilians.
More than 260,000 people have been killed in Syria since the conflict began in March 2011 following a crackdown on anti-government protests.