Syrian government warplanes pounded the northwestern city of Jisr al-Shughur on Sunday, a day after its capture by Al-Qaeda and its allies, a monitoring group said.

The Syrian Observatory for Human Rights said at least four air strikes hit the city, which had been one of regime's last remaining strongholds in Idlib province.

There was no immediate word on any casualties from the latest raids, but the Observatory said the death toll from several dozen air strikes on the city on Saturday had risen to 27.

"At least two civilians and 20 fighters were killed in the Saturday air strikes along with five others whose identities are not yet known," Observatory director Rami Abdel Rahman said.

"The toll is expected to rise after the bombing continued overnight and into Sunday."

Fighting between rebel forces and regime troops continued south of the city on Sunday, he added.

A rebel alliance including Al-Qaeda affiliate Al-Nusra Front seized Jisr al-Shughur on Saturday, less than a month after capturing the provincial capital Idlib city.

State media said government troops had redeployed outside the city "to avoid casualties among innocent civilians."

"Army units carried out night raids against a number of military positions infiltrated by armed terrorist groups in the area surrounding Jisr al-Shughur," the official SANA news agency reported.

It charged that "terrorist groups carried out a horrific massacre of more than 30 civilians, mostly women and children, after entering Jisr al-Shughur."

But it gave no further details of the alleged killings, and the Observatory said it had received no reports of any massacre of civilians.

On Saturday, the Observatory said its sources had seen the bodies of at least 60 regime loyalists in the streets of Jisr al-Shughur after the battle for the city.

It said at least 23 prisoners had been summarily executed by government forces before their withdrawal.

Al-Nusra posted photographs on its official Twitter account of what it said were the bodies of the slain prisoners.

More than 220,000 people have been killed in Syria since the conflict began in March 2011 with anti-government protests that escalated into an armed rebellion.