Most of Idlib and parts of Aleppo province are still controlled by factions opposed to President Bashar al-Assad's Russian-backed regime, including a group that includes onetime members of Al-Qaeda's former Syria franchise.

Five civilians from the same family were killed in Saraqeb and three others in the town of Arnaba, the Syrian Observatory for Human Rights said.

"The region is witnessing very intense bombardment by Russian warplanes," Rami Abdel Rahman, the head of the Britain-based monitoring group, said.

Idlib province is a dead end for people displaced from other formerly rebel-held parts of the country that government forces have retaken.

The violence in northern Syria is escalating an already dire humanitarian situation, with aid groups warning of displacement on an unprecedented scale.

According to the UN humanitarian coordination agency OCHA, almost 350,000 people have fled their homes since December 1, mainly northwards from southern Idlib, which has borne the brunt of the air strikes.

The International Rescue Committee has warned another 650,000 people, mostly children and women, could be forced from their homes if the violence continues.