Clashes pitting mainly jihadist and rebel fighters against regime forces backed by Russian warplanes killed at 66 people on the edge of Syria's northwestern Idlib province, a monitor said Friday.
Among the victims were at least 19 civilians killed by air strikes, the Britain-based Syrian Observatory for Human Rights said, adding that the casualties were over 24 hours of fighting in an area straddling Idlib and Hama provinces.
The head of the Observatory, Rami Abdel Rahman, said seven children were among the civilian victims.
He said 27 soldiers and members of allied paramilitary units were killed in the fighting as well as 20 anti-regime combatants, from Islamist rebel groups the former Al-Qaeda affiliate Fateh al-Sham.
The fresh violence in the area appeared to signal the initial phase of a major government operation against Idlib, the only province in the country that completely escapes regime control.
An AFP correspondent near the fighting said aerial activity was intense and the entire area rocked by frequent air strikes.
Rebel leaders issued warnings through loudspeakers informing remaining civilians in the area that Friday prayers were cancelled and that all residents should stay home.
Hundreds of civilians fled the scattering of villages in the area, creating queues of cars and pickup trucks heading towards the city of Idlib loaded with bags and furniture.