ARIHA: At least 18 civilians were killed on Monday as Syria's regime intensified its bombardment of Idlib province, the last jihadist stronghold in the country's northwest, a monitor said.

Idlib and parts of the neighbouring provinces of Aleppo, Hama and Latakia are under the control of Hayat Tahrir al-Sham, a jihadist group led by Syria's former Al-Qaeda affiliate.

Eighteen civilians, including six children, were killed on Monday in air strikes and missile attacks on Idlib province, said Rami Abdel Rahman, director of the Syrian Observatory for Human Rights.

Ten of them, including four children, died in the town of Ariha, he told AFP, adding that at least 47 people were wounded across the province.

The deaths come a day after regime air strikes killed 12 civilians in the same province, according to the Britain-based Observatory.

An AFP correspondent in Ariha said White Helmet first responders were seen searching for survivors in the rubble of a building hit in Monday's bombardment.

"It was indescribable. Wounded women and children lying on the ground, destruction everywhere, shops damaged," Mohamad Said, a resident at the site of the raid, told AFP.

The first responders were lifted to an upper floor of the badly damaged building in the bucket of an excavator machine in an attempt to rescue a child who had been buried under blocks of concrete.

But the child was among those who died, the AFP correspondent said.

The Observatory says more than 250 civilians have been killed in the spike in violence since the end of April.

More than 200,000 civilians have already been displaced by this upsurge of violence, the United Nations has said.

Idlib is supposed to be protected from a massive government offensive by a September buffer zone deal, but the jihadist bastion has come under increasing bombardment by the regime and its Russian ally since late April.

The pro-government forces have since recaptured several towns in the south of Idlib province and the north of Hama.

The UN has warned an all-out offensive on the northwestern region would lead to a humanitarian catastrophe for its nearly three million residents.

A total of 20 health facilities have been hit by the escalation -- 19 of which remain out of service, according to the UN.