BEIRUT: Syrian troops bombarded rebel bastions on the outskirts of Damascus before dawn on Tuesday while fighting had erupted for control of the northwestern town of Mastuma, activists said.

Troops shelled the towns of Maliha and Beit Saham to the southeast of the capital near the Damascus airport road and the town of Douma to the northeast, the Britain-based Syrian Observatory for Human Rights said.

It said that army reinforcements were also arriving at Daraya in a bid to regain control of the town, where hundreds were killed in August in the bloodiest massacre of the 21-month conflict.

The Local Coordination Committees (LCC), a network of opposition activists on the ground, reported that Daraya and nearby Moadamiyet al-Sham came under heavy shelling from the elite Fourth Division and Brigade 105 stationed in the area.

A military source told AFP that a rocket-propelled-grenade hit an armoured troop carrier on Monday in the orchards west of Moadamiyet al-Sham, causing casualties.

Analysts say the Syrian regime is focused on maintaining its grip on the key axis stretching from Damascus to the central province of Homs and on to the coastal Alawite heartland after its forces were driven from large swathes of territory in the north and east by rebels.

The Observatory said that in the northwest province of Idlib, displaced residents of the town of Mastuma reported troops storming the area during the night, clashing with rebels and executing a number of local men.

A military source had earlier told AFP that the army drove rebels out of Mastuma, just south of Idlib city, with the support of a "special tasks battalion".

The Observatory said fighting for control of the town was still raging.

"There were fierce clashes starting from last night and they are continuing this morning. For sure there were people killed in clashes and by execution but we are not sure how many," Observatory director Rami Abdel Rahman told AFP.

The residents said that snipers had been deployed throughout the town and that troops were stationed in the nearby Baath party camp, which according to the Observatory was turned into a military detention centre in the summer of 2011.

Abdel Rahman noted that the detention centre was a strategic target for its stores of tanks and weapons.

Elsewhere in the province, a military source said that clashes had erupted around the strategic Wadi Deif base, which has been under attack since opposition fighters took over the nearby town of Maaret al-Numan in early October.

Tuesday's violence comes after 78 people were killed nationwide on Monday -- 48 civilians, 18 rebels and 12 soldiers -- according to the Observatory, which collects information from a network of medics and activists on the ground.

The United Nations estimates more than 60,000 people have been killed since a brutal crackdown by President Bashar al-Assad's forces on peaceful protests 21 months ago stirred the violence.