A Syrian warplane bombed a building in the northern rebel-held town of Al-Bab in Aleppo province on Monday, killing at least 10 men, six women and two children, a watchdog said.

Violence also flared in the capital Damascus, where rebels said they are going back on the offensive after being pushed back by regime forces, and in the northwestern province of Idlib, where four troops were killed in clashes, according to the Syrian Observatory for Human Rights.

Among the dead in the Al-Bab strike were a girl and a boy, Rami Abdel Rahman, director of Britain-based Observatory, said. "They died when the fighter jet bombed the building where they were sheltered.

The Syrian Revolution General Commission, a network of activists on the ground, said the toll was likely to rise.

"There are still people stuck in the rubble but nobody can go and help them because the aerial attacks have not ceased," it said.

The airstrike on Al-Bab followed a series of attacks on towns and villages in the Aleppo countryside, as regime forces fight to break rebel supply lines into the city.

The army also pounded several districts of the city of Aleppo, the Observatory said, more than six weeks after the start of what President Bashar al-Assad's regime warned would be "the mother of all battles" in Syria's commercial hub.

State news agency SANA said on Monday that "our brave armed forces continued to pursue terrorists... who sustained heavy losses," adding that the army "seized large quantities of arms and ammunition" from the rebels on the outskirts of Aleppo city.

The army, SANA said, destroyed a number of pick-up trucks equipped with heavy machine guns at Kafr al-Hamra, "at the northern entrance of Aleppo, while terrorists tried to enter the city."

In Damascus, army shelling killed a man and a woman and injured their child in the southern district of Al-Hajar Al-Aswad, according to the Observatory.

Although fighting in Damascus reached its peak mid-summer, violence has persisted as the army attempts to root out pockets of rebel resistance from key districts.

Fighting in the eastern Ghuta area of the province of Damascus raged on Monday, said the spokesman for the rebel Free Syrian Army's Military Council in Damascus.

"The FSA is still relying on hit-and-run tactics, but it has moved on to being on the offensive," Ahmed al-Khatib said via Skype.

"The FSA's mobility in Damascus has increased, and its battalions have a high capacity to penetrate the security forces now," Khatib said.

The Ahfad al-Rasul (grandchildren of the prophet) rebel group meanwhile claimed responsibility for a bombing attack on central Damascus on Sunday, and said the bombs were planted by members of the security forces who had been "bribed" by the rebels.

Fighting in the northwestern province of Idlib saw four regime troops killed and two army vehicles destroyed, the Observatory said.

The watchdog in a very preliminary toll said 38 people were killed nationwide on Monday, 20 of them civilians. It added that 132 people died in violence on Sunday.

More than 26,000 people have died in Syria since the outbreak of an anti-regime revolt in March last year, according to Observatory figures.

The army's crackdown on dissent was so brutal that, several months after it began, the uprising transformed into an armed insurgency.