Sudan's paramilitary Rapid Support Forces (RSF) have allegedly committed numerous crimes against humanity during their siege of the city of el-Fasher in Darfur, UN investigators say.

The report by the UN Fact-Finding Mission accuses the group of "murder, torture, enslavement, rape, sexual slavery, sexual violence, forced displacement and persecution on ethnic, gender and political grounds".

It also cited broader evidence of alleged war crimes by both the RSF and the regular army, however both sides have previously denied any wrongdoing in the country's ongoing civil war.

The UN report said the two groups targeted civilians in numerous ways and as deliberate strategies.

"Both sides have deliberately targeted civilians through attacks, summary executions, arbitrary detention, torture, and inhuman treatment in detention facilities, including denial of food, sanitation, and medical care," said Fact-Finding Mission chair, Mohamed Chande Othman.