The strike hit the village of Jaballa 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.

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.

The Idlib region, which is home to some three million people including many displaced by the eight-year war, is controlled by Syria's former Al-Qaeda affiliate.

Syrian President Bashar al-Assad's forces launched a devastating military campaign against Idlib in April, killing around 1,000 civilians and forcing more than 400,000 people to flee their homes.

But a ceasefire announced by the regime's major backer Moscow has largely held since late August, though the Observatory says skirmishes persist.

On Friday, 23 regime fighters, as well as 11 jihadists and allied rebels, were killed in clashes on the western edges of the Idlib region.

Assad last week said Idlib was the main front remaining to end the civil war, as he made his first trip since 2011 to visit troops in the region.

He spoke as his forces were deploying in Kurdish-majority areas to the east of Idlib to help stave off a deadly Turkish offensive.

Syria's war has killed 370,000 people and displaced millions from their homes since beginning in 2011 with the brutal repression of anti-Assad protests.