"Twenty civilians, including 16 children, were killed in an air strike in Kafr Batikh in Idlib province," the Syrian Observatory for Human Rights said.

Rami Abdel Rahman, the head of the Britain-based monitoring organisation, said the strike hit near a checkpoint held by Hayat Tahrir al-Sham, a jihadist group that consists largely of ex-members of a former Al-Qaeda affiliate.

It was not clear whether the air strike was carried out by the Syrian regime or its Russian ally.

Abdel Rahman said the strike hit children coming out of a nearby school.

"The oldest among them is 11," he said.