Russia has over the years repeatedly struck Syria's last main opposition bastion, but attacks killing civilians had been limited this year until an uptick in violence in late June.

"Russian air strikes this morning" to the west of Idlib left "three dead from the same family" including a woman and a child, and six others wounded, said the Syrian Observatory for Human Rights.

Four strikes hit the area where rebel bases are also present, added the Britain-based group which relies on a network of sources on the ground in Syria.

An AFP correspondent saw a partially destroyed building with floor mats, mattresses and the remains of a vehicle among the rubble.

With Russian and Iranian support, the government of Syrian President Bashar al-Assad has clawed back much of the territory it had lost to rebels early in the conflict that erupted in 2011.

The last pockets of armed opposition to the Assad government include swathes of rebel-held Idlib province, controlled by jihadist group Hayat Tahrir al-Sham (HTS), which is led by the country's former Al-Qaeda affiliate.

Abdul Kafi Kyal, a volunteer with the White Helmets rescue group at the site of the Saturday's strike, condemned the Russian raid which he said caused not only casualties but also spread "terror and panic among civilians".

Syria's 12-year-long war broke out after the repression of peaceful anti-government demonstrations escalated into a deadly conflict that pulled in foreign powers and global jihadists.

The war has killed more than half a million people and displaced millions.

Since 2020, a ceasefire deal brokered by Damascus ally Moscow and rebel-backer Ankara has largely held in Syria's northwest, despite periodic clashes.

However, on June 25, Russian air strikes killed at least 13 people including nine civilians in Idlib province, in what the Observatory said at the time was the deadliest such attack on the country this year.

And on June 28, Damascus's defence ministry said Syrian and Russian forces had launched air strikes on rebel bases "in response to daily and repeated attacks... on civilians" in nearby Hama province.

The announcement came a day after Russian air strikes killed eight HTS-affiliated fighters, according to the Observatory.

The rebel-held Idlib region is home to about three million people, around half of them displaced from other parts of the country.