Sudan's paramilitary Rapid Support Forces have committed multiple crimes against humanity during the siege of al-Fashir in the western Darfur region, a UN-mandated mission said on Friday.

Those come on top of atrocities by both the RSF and its enemy, Sudan's army, in a broader civil war now in its third year, the mission said in a report that strengthened earlier findings.

Neither side immediately responded to requests for comment. Both have dismissed past accusations from the US and rights groups, and have accused each other of carrying out abuses.

"The RSF has further committed crimes against humanity, including large-scale killings, sexual and gender-based violence, looting, and the destruction of livelihoods — at times rising to persecution and extermination," the chair of the fact-finding mission, Mohamed Chande Othman, said in a statement.

The three-person UN team is mandated by the UN Human Rights Council to investigate abuses. It said it based its latest report on more than 200 interviews, many of them with survivors of violence, as well as video material and submissions from civil organisations.

Hundreds of thousands of people have been living under siege in the Sudanese army's last holdout in al-Fashir, capital of North Darfur state, now the frontline of the conflict.

The 18-page report, 'A War of Atrocities', says the RSF and allies have used starvation as a method of warfare there, depriving civilians of relief items such as food and medicine.

The war erupted in April 2023 when the army and the RSF, then partners in power, clashed over plans to integrate their forces.