Warplanes have hit a convoy of civilians fleeing along a major Syrian highway, rescuers and a witness said on Saturday.
It took place in an area where Syrian and Iranian-backed troops were pushing, with air cover, towards a rebel-held town in northwestern Idlib province, they said.
Syrian soldiers and Iranian-backed militiamen were now around 12 km from Saraqeb, advancing towards the Damascus-Aleppo highway under cover of heavy Russian air strikes, two opposition sources said.
Rescuers said at least seven civilians were pulled out of the wreckage of cars after the air strikes on Friday.
"We believe two Russian planes struck the convoy of civilians on the highway and left at least seven killed and 12 injured, mostly elderly and children," said Ammar al Adnan, a civil defence worker from Saraqeb.
Activists' videos on social media showed rescuers extinguishing fires on the route, used by thousands of villagers fleeing areas south of Aleppo now overrun by the Syrian army and its allies.
Reuters could not verify the authenticity of the footage.
A Syrian monitoring group and the media arm of al-Qaida-linked militants are reporting intense airstrikes on a rebel-held stronghold in Syria's northwest.
The Britain-based Syrian Observatory for Human Rights reported more than 35 airstrikes on Saraqeb since late Friday, adding that many of its residents are fleeing.
The Ibaa News Agency of the al-Qaida-linked Levant Liberation Committee, said Russian and Syrian warplanes and helicopter gunships have been pounding Saraqeb and Tel Mardeekh village in Idlib province since the early hours of Saturday.
Syrian government forces and their allies pushed into Idlib, an opposition stronghold, inching closer to a key highway that connects Syria's two largest cities, Damascus and Aleppo.
The UN says more than 270,000 have been displaced in Idlib because of the government onslaught since December 15.
Russia's defense ministry regularly says it is attacking hardline Islamist militants. It denies opposition and witness accounts that its planes target civilians, market places, medical centers and residential areas away from frontlines.
Syrian media made no mention of the strikes.
Syrian army offensive
A major Syrian army offensive, begun earlier this year in southern Aleppo and eastern Idlib, has allowed it to take control of a large amount of territory from rebel forces.
The advances have caused an exodus of thousands of civilians to the relative safety of territory further north towards the Turkish border.
Air raids have struck several cave hospitals and exacerbated a refugee crisis along the Turkish frontier, where camps now house tens thousands of displaced people.
The army confirmed new gains on Saturday, saying it had seized a string of villages from al Qaeda fighters, state television said, quoting a military source.