In a briefing to the UN Security Council, Nazhat Shameem Khan said it was the "assessment of the office of the prosecutor that war crimes and crimes against humanity" had been committed in the RSF's takeover of the city of El-Fasher in October.

"Our work has been indicative of mass killing events and attempts to conceal crimes through the establishment of mass graves," Khan said in a video address, citing audio and video evidence as well as satellite imagery.

Since April 2023, a civil war between the Sudanese army and the RSF has killed tens of thousands, displaced 11 million and created the world's largest displacement and hunger crisis.

Reports of mass killings, sexual violence, abductions and looting emerged in the wake of the RSF's sweep of El-Fasher, which was the army's last holdout position in the Darfur region.

Both warring sides have been accused of atrocities throughout the war.

Footage reviewed by the ICC, Khan said, showed RSF fighters detaining, abusing and executing civilians in El-Fasher, then celebrating the killings and "desecrating corpses".

According to Khan, the material matched testimony gathered from affected communities, while submissions from civil society groups and other partners had further corroborated the evidence.

The atrocities in El?Fasher, she added, mirror those documented in the West Darfur capital of El?Geneina in 2023, where UN experts determined the RSF killed between 10,000 and 15,000 people, mostly from the Massalit tribe.

She said a picture was emerging of "appalling organised, widespread mass criminality".

"It will continue until this conflict and the sense of impunity that fuels it are stopped," she added.

Khan also issued a renewed call for Sudanese authorities to "work with us seriously" to ensure the surrender of all individuals subject to outstanding warrants, including former longtime president Omar al?Bashir, former ruling party chairman Ahmed Haroun and ex?defence minister Abdul Raheem Mohammed Hussein.

She said Haroun's arrest in particular should be "given priority".

Haroun faces 20 counts of crimes against humanity and 22 war-crimes charges for his role in recruiting the Janjaweed militia, which carried out ethnic massacres in Darfur in the 2000s and later became the RSF.

He escaped prison in 2023 and has since reappeared rallying support for the Sudanese army.

Khan spoke to the UN Security Council via video link after being denied a visa to attend in New York due to sanctions in place against her by the United States.