The Russian army said the air raids overnight on the town of Kafranbel, in Idlib province, came after it pinpointed the area as the launchpad for rocket fire on its key Syria airbase of Hmeimim.

Syria's former Al-Qaeda affiliate, Hayat Tahrir al-Sham, controls a large part of Idlib province as well as parts of neighbouring Aleppo, Hama and Latakia provinces.

The jihadist stronghold is supposed to be protected from a government offensive by a September buffer zone deal, but regime and Russian bombardment has increased there since late April.

The Syrian Observatory for Human Rights said Russian air strikes overnight killed five children, four women, and one man in Kafranbel.

The raids hit near a hospital in the town, knocking it out of service, the Britain-based monitor said.

An AFP correspondent saw five homes on the edges on the town that were destroyed or damaged after the strikes.

Survivors picked through the debris to save the belongings they could, the reporter said, while a young man covered in dust from head to toe leant against a wall, shell-shocked after his father was killed.

Umm Wasel narrowly missed the air strike on her home after relatives invited her over to break her daily fast of the Islamic month of Ramadan with them.

"I came back at night to find my home devastated," said the 72-year-old, dressed in a long red robe and a black scarf covering her hair.

People "had thought I was under the rubble", she said.

- Children killed at school -

The Observatory said six other civilians also died in bombardment by regime forces in other parts of the Idlib region on Sunday.

Fighting raged in the north of Hama province between loyalists and jihadists early Monday, the Observatory said, after relative respite in bombardment over the past three days.

Russian aeroplanes pounded the south of Idlib province, while government aircraft targeted the north of Hama province with machine guns, missiles, and crude barrel bombs, the monitoring group added.

Save the Children said 38 children had been killed in shelling in northwest Syria since April 1, including nine at school, seven at the market and one in hospital.

"Schools, hospitals and other vital civilian infrastructure must be protected from attack," the charity's Syria director Sonia Khush said.

"Children are particularly vulnerable to the impact of explosive weapons, and warring parties should make a particular effort to protect them," she said.

The deadly Russian air strikes come after Moscow on Sunday said Syrian armed forces had "unilaterally ceased fire in the Idlib de-escalation zone" from May 18 at midnight, but that fire of loyalists had continued.

Russia and rebel ally Turkey inked a buffer zone deal to protect the Idlib region of some three million people in September, but regime fire has increased there since HTS took control in January.

Syria's war has killed more than 370,000 people and displaced millions inside Syria and abroad since starting in March 2011 with a crackdown on anti-government protests.