Nine children were among those killed when the strikes hit the Zardana area of Idlib province late Thursday, the Syrian Observatory for Human Rights said.

Observatory head Rami Abdel Rahman said the toll was rising because more bodies had been found under the rubble of houses destroyed in the air strikes. Dozens were wounded, he said.

The Russian defence ministry dismissed the Observatory's reports of strikes on Zardana as having "nothing to do with reality", in a statement carried by Russia's TASS news agency.

Zardana is largely controlled by Islamist rebels, with a small presence of the Hayat Tahrir al-Sham alliance led by Syria's former Al-Qaeda affiliate.

An AFP correspondent at the scene saw volunteers with a crane still searching the rubble.

Half a dozen men in civilian clothes helped carry a person in a black body bag away from the site of the strikes, which pulverised several buildings.

Most of Idlib province is held by an array of Islamist and jihadist groups with only parts controlled by the Russian-backed government.

Since Russia intervened in its support in 2015, the government has regained control of around half of the country, driving back rebels.

More than 350,000 people have been killed in the Syrian war since it started in 2011 with the brutal repression of anti-government protests.

The Observatory says it relies on sources inside Syria for its information, and determines who carried out strikes on the basis of flight patterns, and the type of aircraft and ammunition used.