At least seven children and two pregnant women were killed in an air strike on Syria's rebel stronghold province of Idlib on Tuesday, a monitor said.

The strike, which hit the town of Khan Sheikun, in the south of the province, appeared to have been carried out by Syrian government ally Russia, the Syrian Observatory for Human Rights monitor said.

The Britain-based group, which relies on a network of sources inside Syria for its information, says it determines what planes carried out raids according to their type, location, flight patterns and the munitions involved.

In Moscow, the defence ministry denied that Russian aircraft had been in the area on Tuesday, and accused the Observatory of "information provocations".

Russia began its air campaign in support of the government in September 2015, saying it was targeting "terrorists."

"The strike hit a street where children were playing. Three of the dead children were from one family and were visiting their grandfather," Observatory director Rami Abdel Rahman said.

He said the dead children were four girls and three boys, but did not immediately have their ages.

Also in Idlib Tuesday, 11 civilians including three children were killed in air raids and regime bombardment of a village in the southwest of the province, the Observatory said.

Idlib province is mostly controlled by a rebel alliance known as the Army of Conquest, which groups Islamist factions with jihadists of the Fateh al-Sham Front, formerly Al-Qaeda's Syrian affiliate.

Fateh al-Sham is blacklisted by the United Nations and the United States as a "terrorist organisation" and Russ1ia says its fighters are a legitimate target.

Elsewhere, Syrian state media said government forces had advanced southwest of divided second city Aleppo, seizing the 1070 district from rebel forces.

Abdel Rahman also reported the advance, saying it would allow government forces to protect areas already under their control on the southern outskirts of Aleppo.

Rebels have sought to penetrate regime territory on the southern outskirts of Aleppo to end the government siege of the opposition-held east of the city.

The Observatory said that regime forces on Tuesday retook Minyan district in the west from rebels.

Aleppo has been divided between government control in the west and rebel control in the east since mid-2012, but in recent months regime troops have surrounded the east, laying siege to it.

No aid has reached rebel districts, where more then 250,000 people live, since July, and rebels have tried several times to break through government lines to relieve the crippling blockade.