They said security forces opened fire on activists and ordinary civilians on Thursday as they conducted raids in search of dissidents in areas including the capital Damascus, Deir al-Zour, Idlib, Hama and Homs, which has emerged as the epicentre of the uprising.

The Local Co-ordination Committees, an activist coalition, also reported civilians killed in these areas.

There were reports of deadly clashes between army defectors and soldiers near the eastern city of Deir al-Zour and near Maarat al-Numan, a town on the highway linking Damascus and the major city of Aleppo.

This comes as new video emerged on the internet of Syrian soldiers coming under fire from some apparently heavily armed opposition fighters.

The footage, reportedly shot on Sunday, seems to add to claims that suggest opposition groups are arming themselves in the fight against government forces.

Syria has barred most foreign media, making it difficult to verify death tolls as well as accounts from activists and officials.

It is difficult to gauge how many people have defected from the army and what kind of threat they pose to the government. Although the crackdown has led to broad international isolation of Assad, he appears to have a firm grip on power, retaining the loyalty of most of the armed forces.