"Intense clashes took place in the districts of Bab al-Hadid, Zahraa, Arkub and Al-Hindrat Camp as explosions were heard and aircraft were sighted overhead," the Syrian Observatory for Human Rights said.

Helicopter gunships flew over the Saif al-Dawla district as well as Salaheddin, where rebels held off an offensive by ground troops backed by tanks and helicopters on Saturday, the Britain-based watchdog said.

In the central city of Homs, a battle broke out near the police headquarters between troops and rebel fighters, of whom at least one was killed.

Near the capital, sniper fire killed a civilian in the town of Irbin, the Observatory said. Two more were killed in shelling in Idlib province in the northwest.

On Saturday, violence killed 168 people 94 civilians, 33 rebels and 41 soldiers, the Observatory said.

More than 20,000 people have died in Syria since the uprising against President Bashar al-Assad's rule broke out in March last year, according to the watchdog's figures

It is not possible to check casualty tolls independently in Syria. The United Nations has a troubled military observer mission in the country but has stopped giving figures for the overall death toll.