BEIRUT: Syrian regime and Russian bombardment has killed 20 civilians including seven children in northwestern Syria, a war monitor said Saturday, in the latest deadly raids on the embattled opposition bastion.

Regime warplanes and helicopters late Friday carried out air strikes on Mahambel village in Idlib province, killing 13 civilians including the seven children, the Syrian Observatory for Human Rights said.

Another seven civilians were killed Saturday, including a woman hit by regime rocket fire on the outskirts of the town of Khan Sheikhun in the south of the province, the Britain-based war monitor said.

Three members of a family were killed by a Russian air strike on the town of Morek, in neighbouring Hama province, the Observatory reported.

Idlib, a region of some three million people, many of whom fled former rebel-held areas retaken by the government, is the last major bastion of opposition to the Russia-backed Damascus government after eight years of civil war.

The region on Turkey's doorstep is administered by Syria's former Al-Qaeda affiliate Hayat Tahrir al-Sham, but other jihadist and rebel groups are also present.

Idlib is supposed to be protected from a major regime assault by a September deal between Moscow and Ankara, but Damascus and its Russian ally have ramped up their deadly bombardment of the region since late April.

More than 530 civilians have been killed since then, according to the Observatory.

The United Nations says 25 health facilities in the region have been hit, the latest including the second attack in two months on an underground hospital in the town of Kafranbel on Thursday.

"The attacks happened despite the fact that the coordinates of this hospital had previously been shared with the parties to the conflict in a deliberate, carefully planned effort to prevent any attacks on it," an UN official said on Friday.

"I am horrified by the ongoing attacks on civilian areas and civilian infrastructure as the conflict in northwest Syria continues," said Mark Cutts, UN deputy regional humanitarian coordinator for the Syrian crisis.

Syria's war has killed more than 370,000 people and displaced millions since it started in 2011 with a brutal crackdown on anti-government protests. —AFP