At least two barrel bombs hit the largest hospital in the rebel-held side of Syria's Aleppo city on Saturday, the medical organisation that supports it said.

"Two barrel bombs hit the M10 hospital and there were reports of a cluster bomb as well," said Adham Sahloul of the Syrian American Medical Society.

Both M10 and the second-largest hospital in the area, M2, had already been hit by heavy bombardment on Wednesday that UN Secretary General Ban Ki-moon denounced as "war crimes."