At least 50 people have died after the Syrian army stormed Deir al-Zour, the largest city in the east and a scene of frequent protests, activists say.

Scores of tanks and armored vehicles are reported to have entered several areas of the city after a heavy bombardment that began before dawn.

At least 26 other people have been killed in Homs province and six in Idlib in the north-west, BBC reported.

President Bashar al-Assad has defended his security forces' deadly crackdown.

"Syria is on the path to reform," he was quoted as telling Lebanese Foreign Minister Adnan Mansour by the state news agency, Sana. "To deal with outlaws who cut off roads, seal towns and terrorise residents is a duty of the state, which must defend security and protect the lives of civilians," he added.

Activists say at least 1,650 civilians have been killed and tens of thousands arrested since the uprising began in mid-March.