The UN’s migration agency says around 700 people were killed in Sudan’s West Darfur region following clashes between the army and the Rapid Support Forces (RSF).
The incident happened late last week in El Geneina where 300 more are reported missing.
A local human rights organisation estimates that as many as 1,300 were killed in West Darfur since last Friday and blames the RSF for the atrocities.
This comes as the RSF appears to be gaining momentum in the region.
Witnesses accuse the paramilitary group and its allies of targeting non-Arabs in the areas it has captured.
The Roots Organization for Human Rights and Violations Monitoring, a group advocating for rights in West Darfur, accuses the RSF of raiding displacement camps and launching attacks.
The RSF had previously denied similar accusations.
According to relief agencies thousands have fled to neighbouring Chad in recent days.
More than five and a half million are estimated to have been pushed out of their homes since violence between the RSF and the Sudanese Armed Forces broke out in April.