The Syrian Network for Human Rights said armed groups and foreign fighters aligned with the government but not integrated into it were largely responsible for the sectarian violence.

A war monitoring group said more than 1,000 were killed in revenge attacks and clashes between Syrian security forces and loyalists of ousted President Bashar Assad.

A war monitoring group said on Saturday that the violence was one of the deadliest incidents since Syria's conflict began 14 years ago.

Sunni Muslim gunmen loyal to the government launched retaliatory attacks against members of the Alawite sect, to which Assad belongs.

The death toll from two days of clashes between security forces and loyalists of ousted Syrian president Bashar al-Assad and revenge killings that followed has risen to more than 1,000, including nearly 750 civilians,