Russian jets bombed camps near the northwestern Syrian city of Idlib on Sunday, killing at least nine civilians, in a new attack on the last opposition stronghold, witnesses and rescue workers said.

High-altitude fighters backed by Syrian army artillery also dropped bombs on forests near temporary camps west of Idlib, witnesses said.

So far, there have been no claims of an attack by Russia or its allies in the Syrian army, which has previously said it was targeting rebel group hideouts and denied attacking civilians.

The opposition Civil Defense Service said three children and a woman were among those killed in the strikes on the overcrowded camps, where more than 70 people were injured and taken to field hospitals.

“There are no military bases, warehouses, or rebel barracks here. Only civilians,” Seraj Ibrahim, a rescuer for the so-called White Helmets, who are backed by the West, said by phone.

More than 4 million people live in the densely populated and opposition-held northwest along the border with Turkey. Most of them were driven there by successive Russian-led campaigns that reclaimed territory seized by the rebels.

Last month, Russian jets struck areas controlled by the Hayat Tahrir al-Sham jihadist group after a series of battles between rival rebel forces in the northwest, in fresh strikes that shattered the relative calm that has lasted since the beginning of this year.

The region has been hit by sporadic shelling from the Syrian army on the front line. The rebels also bombed the territories under their control.

A deal reached nearly three years ago between Russia, which backs Syrian President Bashar al-Assad’s forces, and Turkey, which backs opposition groups, ended months of fighting that displaced more than a million people.