At least 15 civilians have been killed in a barrel bomb attack on a wake being held for children who died in earlier air strikes in the rebel-held Syrian city of Aleppo.

Hospital officials said suspected government helicopters dropped bombs in the Bab al-Nairab area, and it is feared the death toll will increase.

Mohammed Khandakani, a hospital volunteer, said one of those injured told him a barrel bomb was dropped as people paid their respects to 11 children killed on Thursday in an air strike in the same area.

Minutes later, another barrel bomb was dropped, injuring an ambulance driver and hampering rescue efforts.

The Syrian government and its Russian ally are the only ones operating helicopters over Aleppo. The government denies it uses barrel bombs.