A maternity hospital supported by Save the Children was bombed in an air raid in Idlib province of northwest Syria, causing casualties and heavy damage, the Britain-based charity said.

"Save the Children-supported maternity hospital in Idlib bombed, casualties reported - numbers unconfirmed," it said on Twitter.

The Syrian Observatory for Human Rights also said that the hospital in the rebel-held town of Kafar Takharim was heavily damaged and left barely operational.

The monitoring group did not specify if the raid was carried out by Syrian regime aircraft or warplanes of its Russian allies.

The bombing "hit the entrance to the hospital, which is the biggest in the area, serving over 1,300 women monthly and carrying out over 300 deliveries a month", Save the Children said in an email.

"This is the only hospital specialising in maternity and children in the northern western side of rural Idlib."

Last week, air raids struck four makeshift hospitals and a blood bank over a 24-hour period in the regime-besieged eastern sector of the city of Aleppo.

In Aleppo, at least 10 civilians were killed, including five children, in air strikes on the rebel-held town of Atareb, a monitor said.

The Syrian Observatory for Human Rights said three strikes targeted the main road and centre of the town, warning the death toll could rise because of a large number of seriously wounded.

It was unclear if Syrian regime warplanes or aircraft of its Russian allies carried out what the Observatory called "a new massacre" that left children dismembered.