Overnight airstrikes killed 28 people, including four children, in a village in rebel-held Idlib province, the Syrian Observatory for Human Rights said on Saturday.
Rescue workers have said Syria and Russia have killed scores of civilians in airstrikes that began after insurgents launched an offensive against government-held areas in the northwest of the country on Sept. 19.
The Russian and Syrian militaries say they only target militants and deny killing civilians.
Dominated by the jihadist group formerly known as the Nusra Front, the Idlib region had seen a six month lull in airstrikes until the latest escalation.
However, the overnight airstrike targeted the village of Armanaz a few kilometres from the Turkish border. The Syrian Civil Defence, a rescue service operating in rebel-held areas, put the preliminary death toll at 26.
Turkey said this week that recent Russian bombing in Idlib had killed civilians and moderate Syrian rebels, saying this violated an agreement concluded with Iran and Russia.
Turkey, Iran and Russia to create a “de-escalation” zone in Idlib. Under the agreement, Turkey will deploy troops in Idlib, Turkish President Tayyip Erdogan has said.