More than 20 air strikes targeted two mountains and three villages in the Jabal al Zawiya region and two other villages in the countryside of the Hama province, a war monitor and a civil defence group said.
Russia carried out air strikes in the de-escalation zone in Idlib, Syria, killing at least three civilians and injuring three others, a Syrian civil defence group said on Monday.
The White Helmets civil defence group said three others were injured in the attacks.
More than 20 air strikes targeted two mountains and three villages in the Jabal al Zawiya region and two other villages in the northwestern countryside of the Hama province, the Syrian opposition aircraft observatory said.
Search-and-rescue efforts are underway in the area.
Idlib falls within a de-escalation zone forged under an agreement between Turkey and Russia.
The area, lying along Turkey's southern border, has been the subject of multiple ceasefire understandings, which have frequently been violated by the Assad regime and its allies.
It is currently home to four million civilians, including hundreds of thousands displaced in recent years by regime forces throughout the war-weary country.
Heavy clashes continue
Moreover, an al Qaeda offshoot led an offensive on Monday against regime forces in northwest Syria, sparking clashes that left 19 pro-Assad fighters and 22 militants dead, a war monitor said.
Extremist factions led by Hurras al Deen launched an assault on two villages in Sahl al Ghab, a region of the central province of Hama, the Syrian Observatory for Human Rights said.
They briefly seized the villages of Al Fatatra and Al Manara, observatory chief Rami Abdel Rahman said.
But Assad forces took them back just hours later amid Russian air strikes and intense shelling, the Britain-based monitor said.