Over 6,000 people were killed over three days in late October when a Sudanese paramilitary group unleashed what the U.N. described as a wave of violence shocking in its scale and brutality across the Darfur region.

The Rapid Support Forces' (RSF) offensive to capture the city of el-Fasher included widespread atrocities that amount to war crimes and possible crimes against humanity, the U.N. Human Rights Office said in a report released Friday.

"The wanton violations that were perpetrated by the RSF and allied Arab militia in the final offensive on el-Fasher underscore that persistent impunity fuels continued cycles of violence," said U.N. High Commissioner for Human Rights Volker Türk.

The RSF and their allied Janjaweed militias, overran el-Fasher, the Sudanese army’s only remaining stronghold in Darfur, on Oct. 26 and rampaged through the city and its surroundings after more than 18 months of siege.

The 29-page U.N. report detailed a set of atrocities that ranged from mass killings and summary executions, sexual violence, abductions for ransom, torture and ill-treatment, to detention and disappearances. In many cases, the attacks were ethnicity-motivated, it said.