Forces loyal to Syrian President Bashar al-Assad have killed seven children during fighting for the town of Nabek, north of the capital Damascus, activists said.

The fighting in Nabek pits Assad's army and allied militia against rebel factions including al-Qaeda-linked fighters.

Images posted on social media showed what activists said were the bloodied corpses of five children and said up to seven had been killed.

Some blamed a Shia militia for the killings, but this could not be confirmed. The rebels are mostly Sunni Muslims.

Nabek is 80 kms north of Damascus on Syria's north-south highway that links the capital to the central city of Homs and the coastal heartland of Assad's minority Alawite sect.

Fighting in the area intensified last month when the government launched an offensive to secure towns along the road. Fighters from the Lebanese Shia group, Hezbollah, joined in on the government side.

Pro-government forces shelled the eastern areas of Nabek and raided homes in western areas as clashes continued on Sunday.

The state news agency SANA made no mention of casualties, but said the army was carrying out operations in the area and had eliminated "armed terrorist groups" around Nabek.

More than 120,000 people have been killed in the year-old conflict and efforts by divided world powers to end the violence have made little progress.