Russian jets bombed camps near Syria's northwestern city of Idlib on Sunday, killing at least nine civilians in a flare-up of attacks on the last opposition-held bastion, witnesses and rescuers said.
War planes flying at high altitude, aided by Syrian army artillery, also dropped bombs on forests near the makeshift camps west of Idlib, witnesses said.
No immediate comment was available from Russia or its allies in the Syrian army, which says it targets the hideouts of insurgent groups and denies attacking civilians.
The opposition civil defence service said three children and a woman were among those killed in the strikes on the crowded camps where more than 70 people were wounded and rushed to field hospitals.
"There are no military bases or warehouses or rebel barracks here. Only civilians," Seraj Ibrahim, a rescuer with the Western-backed White Helmets organization, said when reached by phone.
More than 4 million people live in the densely populated opposition-held northwest area along the Turkish border. Most of them were driven there by successive Russian-led campaigns that regained territory seized by rebels.
Opposition sources said a coalition of armed groups led by the jihadist Hayat Tahrir al Sham organization and another led by mainstream Turkish-backed rebels retaliated by attacking several major Syrian army outposts in the region.
Syrian air forces struck a drones facility and a militant training camp in northwest Syria in response to earlier attacks by armed insurgents, Russia's state-owned news agency TASS reported on Sunday. Syrian state media did not report any fighting.
The Russian defence ministry on Friday said it had information that insurgents it describes as terrorists operating in the Idlib region were plotting an attack on the main Russian air base of Hmeimim in the coastal province of Latakia with the use of unmanned suicide drones.
Russian jets last month hit areas under the control of Hayat Tahrir al Sham after a bout of fighting among rival rebel forces in the northwest in renewed strikes that shattered a relative lull in raids since earlier this year.
The region has been hit by sporadic shelling from Syrian army outposts against frontlines. Rebels have shelled areas under their control.
A deal brokered nearly three years ago between Russia, which backs Syrian President Bashar al Assad's forces, and Turkey, which supports opposition groups, ended fighting that had displaced more than a million people within a few months.
With the help of Russia and Iran, Assad has turned the tide of a war that has lasted more than a decade and regained most of the territory he lost to rebels.
(Reporting by Suleiman Al-Khalidi; Editing by Andrew Heavens and Paul Simao)