Russian and Syrian warplanes flew over and hit some cities in the province of Idlib, in the hands of the Syrian opposition. The day after the summit of the presidents of Turkey, Iran and Russia who failed to agree on a ceasefire that would have prevented the offensive supported by Russia.
Witnesses and rescuers have reported that at least a dozen air strikes have hit a number of villages and towns in the south of Idlib and in the city of Latamneh in northern Hama, where the rebels still have control.
Syrian helicopters dropped so-called barrel bombs - containers filled with explosive material - on civilian homes on the outskirts of the city of Khan Sheikhoun, two residents in southern Idlib said.
Three civilians were killed in Abdeen village in southern Iblib, a civil protection source said.
Friday's summit heralded an impending military operation in Idlib, the last major stronghold of the opposition to the government of President Bashar al-Assad.
Turkish President Tayyip Erdogan pushed for a cease-fire at the summit, but Russian President Vladimir Putin said a truce would be useless as it would not involve Islamic militant groups that Assad and its allies hold terrorists.
Tehran and Moscow have helped Assad change the course of the war against a host of opponents ranging from Western-backed rebels to Islamic militants, while Turkey is a major opposition supporter and has troops in the country. The fear of Turkey is the impending exodus of refugees to its borders.
The United Nations fears a full-scale offensive that could cause a humanitarian catastrophe involving tens of thousands of civilians.