A Syrian military operation against remnants of the former Assad regime has now ended, having sparked some of the worst violence seen in the country in years.

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.

This past weekend’s sectarian violence was possibly among the bloodiest 72 hours in the modern history of Syria after 14 years of civil war — and it threatens to open an endless cycle of vengeance

Armed groups killed entire families, including women and children, during an outbreak of sectarian violence in Syria last week, the United Nations human rights office said on Tuesday.

A monitoring group says 973 civilians have been killed in revenge attacks against the Alawite sect since Thursday.

Entire families including women and children were killed in Syria's coastal region as part of a series of sectarian killings by rival groups during an insurgency by Bashar al-Assad loyalists, the U.N human rights office said on Tuesday.