Britain-based monitor, the Syrian Observatory for Human Rights said the strike hit the village of Jabala in the south of the Idlib region and that the victims were all from a single family.
A Russian air strike killed six civilians, including a child, in the embattled opposition bastion of Idlib in northwestern Syria, a war monitor said.
The strike hit the village of Jabala in the south of the Idlib region, taking the lives of all six from the same family, the Syrian Observatory for Human Rights said.
The Britain-based monitor, which relies on sources inside Syria, says it determines who carries out an air strike according to flight patterns, as well as aircraft and ammunition involved.
A correspondent at the site of the strike saw rescue workers searching a mound of concrete rubble near a surviving olive tree.
Grasping the edges of a thick blanket, six men carried out a victim.
Observatory head Rami Abdel Rahman said it was the bloodiest such Russian air raid in two months since Moscow announced a truce for the surrounding area on August 31.
Since then, eight other civilians have been killed in Russian air strikes on different dates in the region, he said.
In 2018, Turkey and Russia agreed to turn Idlib into a de-escalation zone in which acts of aggression are expressly prohibited.
The de-escalation zone is currently home to some four million civilians, including hundreds of thousands displaced in recent years by regime forces from throughout the war-weary country.
Syria has been locked in a vicious civil war since early 2011, when the Assad regime cracked down on pro-democracy protests with unexpected ferocity.
Since then, hundreds of thousands of people have been killed and more than 10 million others displaced, according to UN officials.