The air strike hit the family's one-story home in the village of Dayr Sharqi in Idlib province, killing everyone inside, said the Britain-based Syrian Observatory for Human Rights.

A photographer collaborating with AFP said he saw a man leaving the site of the blast, carrying the bloody corpse of a young girl, her hair streaked with blood.

A rescue worker carried the dust covered body of a second child, he added.

The photographer said he also saw the charred remains of a third victim trapped underneath the rubble, as rescue workers tried to retrieve it.

Heightened air raids by the Syrian regime and its ally Moscow on the Idlib region -- the last major opposition bastion in Syria's northwest -- have killed hundreds since the end of April.

The latest air strikes on the village of Dayr Sharqi wounded three other people, the Observatory said.

The attack came a day after Russian air raids killed 15 civilians, including six children in a nearby displacement camp in the town of Hass, according to the war monitor.

Two other children were killed by Syrian regime air strikes in different parts of southern Idlib on Friday, it said.

A French foreign ministry statement released after those attacks condemned "indiscriminate air strikes by the regime and its allies in Idlib".

It specifically mentioned the air strikes on the displacement camp and called "for an immediate cessation of hostilities".

Over the past week, regime forces have advanced on the southern edges of Idlib province, with the aim of capturing the town of Khan Sheikhoun, which lies on a key highway coveted by the regime.

The highway runs through Idlib, connecting government-held Damascus with the northern city of Aleppo, which was retaken by regime forces from rebels in December 2016.

Syria's former Al-Qaeda affiliate Hayat Tahrir al-Sham (HTS) has since January controlled most of Idlib province as well as parts of neighbouring Hama, Aleppo and Latakia provinces.

Other rebel groups are also present in the area.

A buffer zone deal brokered by Russia and Turkey last year was supposed to protect the region's three million inhabitants from an all-out regime offensive, but it was never fully implemented.

Regime and Russian air strikes and shelling since late April have killed more than 850 civilians, according to the Observatory.

The United Nations says the violence has displaced more than 400,000 people.

AFP correspondents have reported seeing dozens of families flee fighting over the past few days, heading north in trucks stacked high with belongings.

Syria's conflict has killed more than 370,000 people and displaced millions at home and abroad since starting with the brutal repression of anti-regime protests in 2011