Two children were among six people killed in regime strikes on the town of Kafr Aweid in the jihadist-held province of Idlib, said the Syrian Observatory for Human Rights.

The victims' relatives gathered at the town's graveyard on Wednesday afternoon as an excavator dug a large pit in the ground.

The scattered remains of one of the children were placed in a cardboard box before being buried, an AFP photographer said.

The corpse of another was covered in an embroidered blue sheath.

Another civilian died in regime shelling on the northern Hama countryside, also held by insurgents, said the Britain-based monitor.

Regime air strikes also hit a motorcycle in the Idlib town of Maaret al-Numan, killing a woman and her two children, said the Observatory.

Wednesday's attacks come amid an escalation in violence in parts of the country's northwest held by Syria's former Al-Qaeda affiliate Hayat Tahrir al-Sham.

A September deal was supposed to avert a full-out regime offensive on Idlib province and adjacent areas, home to around three million people, nearly half of whom have been displaced from other parts of Syria.

But the regime and its ally Russia have since late April ramped up deadly air strikes and rocket fire on the region, and fighters have clashed on its edges.

The bombardment of Idlib province and neighbouring areas has killed more than 300 people since late April, according to the Observatory.

It also displaced nearly 270,000 people in May alone, according to the UN.

A total of 24 health facilities and 35 schools have been hit in the latest escalation, according to the UN's humanitarian office.

Analysts predict that President Bashar al-Assad and his allies will continue to chip away at the area, but not unleash a major assault that would create chaos on Turkey's doorstep.

The conflict in Syria has killed more than 370,000 people since it started in 2011.