Geneva, Switzerland - The world must act immediately to halt the "horrific atrocities" in Sudan's El-Fasher, the UN rights chief told AFP Monday, urging countries not to wait until a "genocide" was declared.

The paramilitary Rapid Support Forces (RSF), which has been at war with the regular army since April 2023, captured the last military stronghold in western Darfur on October 26.

Since El-Fasher's takeover after a grueling 18-month siege, the United Nations and rights monitors have reported widespread atrocities, including ethnically-driven killings and abductions.

"It's clear that atrocity crimes are being committed as we speak," UN Commissioner for Human Rights Volker Turk told AFP in an interview, stressing that the siege had in itself been "an atrocity crime."

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"People were beleaguered and under siege, under horrific conditions, no food, hardly any water... We have reports of people having to eat animal feed, for example, eating peanut shells."

Pointing to the declaration of famine in some parts, he said the situation was "so desperate... with children dying of starvation."

Since the RSF had swept in, Turk said his office had received "credible evidence of mass killing; that when people are trying to flee this horrible situation, they get shot at."

"There are very serious reports of rape and sexual violence and gang rape, (and) we have very serious issues of killings of those who are supposedly collaborators," he said.

Asked if he feared a genocide might be underway, Turk stressed that "whether or not it qualifies for genocide is again for traditional authorities to say."

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But, he insisted, "we shouldn't wait for any of this. We should act now, when these horrific atrocities are being committed as we speak."

"You don't need to wait until the court decides that it's been genocide."

The rights chief said there were fears that the atrocities unfolding in El-Fasher might be repeated in Sudan's oil-rich Kordofan region.

"I hope that the international community really wakes up," he said, lamenting that "all the warnings that we have given over the whole year... were not heeded."

It was vital to ensure there "is not a repeat again of similar things in North Kordofan," he said, cautioning that "the signs for it are extremely worrying."