More than 1,000 people have been killed in clashes in the coastal provinces of Syria, according to one war monitoring group.

The number of people killed in clashes in Syria between government security forces and supporters of ousted former President Bashar al-Assad has risen to 642, according to a monitoring group.

More than 800 civilians belonging to Syria's minority religious Alawite community have been killed in Syria's worst spate of violence since the ouster of long-time dictator Bashar al-Assad around three months ago,

At least 240 people have been killed in northwest Syria as fierce clashes escalate between government forces and loyalists of former President Bashar al-Assad, marking the deadliest violence since the fall of Assad three months ago.

Syrian security forces battled for a second day on Friday to crush a nascent insurgency by fighters from Bashar al-Assad's Alawite sect, with scores reported killed as the Islamist-led government faced the biggest challenge yet to its authority.