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.

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

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.

The killings occurred in the heartland of Syria’s Alawite minority, escalating after a nascent insurgency formed against the Sunni Islamist government.

The UN human rights office has verified the killing of 111 civilians in the coastal region, but says the actual figure is far higher.