BEIRUT — Airstrikes in Syria killed 17 people, mostly children on Wednesday when warplanes struck a school complex in the northern rebel-held province of Idlib, activists said.

The Idlib News network said the strikes hit as the children were gathered outside the school complex in the village of Hass. The activist-operated group put the death toll at 17, and said most of the victims were children.

There were fears the death toll could rise further as some of the wounded were reported to be in critical condition, the network added. Another activist group, the Britain-based Syrian Observatory for Human Rights put the death toll at 22. It said 14 children and a woman were among those killed.

Idlib is the main Syrian opposition stronghold, though radical groups also have a large presence there. It has regularly been hit by Syrian and Russian warplanes as well as the U.S.-led coalition targeting Islamic State militants.

Footage posted by activists on line shows a huge plume of smoke rising from the area of the strikes. Rescuers are seen rushing casualties away along a dusty road lined with destroyed buildings.

A woman’s body is seen being carried on a stretcher while other bodies, covered in cloth and one with only a hat, are lying under shrubs in what could possibly have been a garden among the buildings. Other casualties are seen being ferried in pick-up trucks.

An activist at the scene, Muaz al-Shami, says as many as 10 airstrikes are believed to have hit the residential area.

“I don’t want to go to school anymore,” a young girl says, weeping.

Earlier in the day, the northern Aleppo province saw a new escalation as a helicopter believed to belong to Syrian government forces dropped barrel bombs in a deadly attack on Turkey-backed opposition forces in the border area, Turkish officials said. A statement attributed to the field commander of Syria’s pro-government troops said any Turkish advances in northern Syria under the pretext of fighting IS militants would be dealt with “forcefully and appropriately.”

The barrel bombing was said to have occurred in the village of Tal Madiq, in a part of northern Aleppo where rival groups have been operating, mostly to rout Islamic State militants.

If confirmed, the attack would be the first by Syrian government forces on the Turkish-backed fighters. Turkey’s state-run news agency didn’t say when the attack happened and said at least two Syrian opposition fighters were killed and five others wounded. A Syrian opposition spokesman said it took place Tuesday.

The Observatory’s chief, Rami Abdurrahman, said helicopters struck as intense clashes were underway between Kurdish-led fighters and Turkey-backed forces in Tal Madiq and that 11 Syrian opposition fighters and five Kurdish fighters were killed.