A UN fact-finding mission has determined that evidence of atrocities carried out during the siege and takeover of the Sudanese city of el-Fasher points to genocide.

The paramilitary Rapid Support Forces (RSF) captured el-Fasher, located in the western region of Darfur, at the end of October after an 18-month blockade.

It was one of the most brutal chapters in Sudan's nearly three-year civil war and triggered widespread international outrage.

This is the closest the UN has come to declaring that genocide is being carried out by RSF fighters in Darfur during the current conflict. The RSF has not commented on the report but has denied previous such accusations.

"The body of evidence we collected — including the prolonged siege, starvation and denial of humanitarian assistance, followed by mass killings, rape, torture and enforced disappearance, systematic humiliation and perpetrators' own declarations - leaves only one reasonable inference," said fact-finding mission expert Mona Rishmawi. "The RSF acted with intent to destroy, in whole or in part, the Zaghawa and Fur communities in El-Fasher. These are the hallmarks of genocide."

The report concludes that at least three underlying acts of genocide were committed, including killing members of a protected ethnic group; causing serious bodily and mental harm; and deliberately inflicting conditions of life calculated to bring about the group's physical destruction in whole or in part.

Calling the findings "truly horrific", UK Foreign Secretary Yvette Cooper said she would take the report's conclusions to the UN Security Council on Thursday.

In a statement she said there must be international criminal investigations to ensure accountability for perpetrators and justice for victims, and an end to the arms flow feeding the conflict.

Sudan's civil war erupted in April 2023 out of a power struggle between the regular army and the RSF over how and whether the paramilitaries would integrate into the security forces. It evolved into a country-wide conflict fuelled by longstanding local grievances and ethnic divisions.

In the Darfur region, Arab militias that form the backbone of the RSF have targeted non-Arabs they see as enemies, using savage tactics also employed some 20 years ago. At that time, they massacred hundreds of thousands of Darfuris from indigenous African ethnic groups, employed by the country's then authoritarian leader Omar

The report says the city was deliberately starved and destroyed during the long siege, which systematically weakened the "targeted population" and left them defenceless against the extreme violence that followed.

"Thousands of persons, particularly the Zaghawa, were killed, raped or disappeared during three days of absolute horror," it says, as RSF troops failed to distinguish between Zaghawa civilians and the armed groups defending the city.

Investigators described RSF conduct in el-Fasher as an aggravation of earlier patterns but on a far more lethal scale, noting that this demonstrates the failure to prevent the atrocities despite clear warning signs. They say without prevention and accountability, the risk of "more genocidal acts remains serious and ongoing".

The mandate issued by the Human Rights Council in Geneva called on the investigative team to "identify, where possible" suspected perpetrators in a bid to ensure they are "held accountable".

The report names RSF Leader Lt Gen Mohamed Hamdan Dagalo (widely known as Hemedti) and spokesperson Lt Col Al-Fatih Al-Qurashi, citing the way they publicly claimed and celebrated the operation.

It notes that General Hemedti acknowledged some "violations" had occurred during the takeover of the city but that while he described el-Fasher as a "catastrophe", he justified the assault as necessary.

The RSF leader also issued instructions for his fighters not to harm civilians or kill prisoners, and he promised investigations. But investigators say the RSF did not respond to the mission's request to clarify the steps it had taken, or any other questions.

"The scale, coordination, and public endorsement of the operation by the senior Rapid Support Forces leadership point to a planned and organised operation executed through an established hierarchy and structure, rather than isolated acts," the UN mission said.

The report names one one notorious commander known as "Abu Lulu" who was arrested after viral footage of his brutality surfaced, but said the RSF had provided no information regarding any judicial proceedings.

It also says that despite their best efforts, the UN mission did not receive cooperation from Sudanese authorities. Yvette Cooper called obstructions "from both warring parties... shameful and unacceptable".

The mission's mandate did not include an investigation into the role of external actors who may be supporting the RSF.

But crucially the report notes that the RSF's military campaign was reinforced by foreign mercenaries equipped with "advanced weaponry and communications systems".

It says investigators are engaging with several states regarding "credible information" that they are involved and will report on this matter in the future.

The United Arab Emirates (UAE) is widely reported to be the main backer of the RSF, although it continues to forcefully deny this, despite extensive evidence from international investigations that the UN has previously described as credible.

Abu Dhabi's role came under increased scrutiny after the el-Fasher massacre, but there was no public pressure on the Emiratis from the UN, the US or the UK.

The investigators called on the international community to fully enforce the existing arms embargo on Darfur and expand it to the rest of the country; to prevent the transfer of weapons and other support to parties implicated in serious violations; to ensure accountability through targeted sanctions; to fully cooperate with the International Criminal Court; and to consider the establishment of a judicial mechanism working in tandem with it.

Cooper said it was important that the fact-finding mission planned to conduct further investigations into reported breaches of the arms embargo and agreed that it should be extended and enforced.

She said she planned to highlight the systematic and widespread sexual violence which she calls "a war against women's bodies".

"Most important of all we need global action and pressure in pursuit of a ceasefire, and essential humanitarian access with support for survivors," she said.

The UN Security Council session is aimed at pushing for progress on a humanitarian truce, which has been elusive despite the enormous civilian suffering. The warring parties both frame the conflict as an existential battle and are able to continue fighting with increasingly sophisticated weapons supplied by their foreign backers.

"The world is still failing the people of Sudan," Cooper said. "When the stories started to emerge about the horrors of el-Fasher it should have been a turning point, but the violence is continuing. Today, in the Security Council, the UK as President will make sure the world does not look away."