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“The fighting must stop immediately … It’s incumbent on Sudanese leaders to put the interests of their people front and centre,” he told the UN Security Council in an emergency meeting.
The North African country was plunged into chaos about two weeks ago when street battles erupted between the military and the paramilitary Rapid Support Forces.
More than 450 people have been killed while 4,000 have been wounded, UN figures show.
Mr Guterres said the power struggle was “lighting a fuse” that could detonate across borders, apart from putting Sudan’s future at risk.
He urged UN member states and regional organisations with “influence” to press the warring parties to de-escalate tension and return to the negotiating table “immediately”.
Volker Perthes, the Secretary General's special representative for Sudan, told council members that the 72-hour ceasefire brokered by the US and Saudi Arabia on Tuesday appeared to be holding in some areas.
However, an unequivocal sign that the Sudanese Armed Forces or the RSF are ready to “seriously negotiate” has yet to be seen, he said.
This suggests “that both think that securing a military victory over the other is possible”, Mr Perthes said.
The special representative warned that this was a miscalculation, as Sudan could become “increasingly fragmented”, leading to a devastating impact on the region.
He accused both sides of having a “disregard for the laws and norms of war”, and committing abuses that “may amount to war crimes or crimes against humanity”.
Al-Harith Idris Al Harith, Sudan's ambassador to the UN, expressed gratitude following international efforts to try to resolve the situation but said his country would find its own way through the crisis.
“We express our appreciation for the efforts of brotherly and friendly countries and regional organisations to help calm the situation,” he said.
“This matter is an internal matter that should be left to the Sudanese to find the required solutions amongst themselves”.
Lana Nusseibeh, the UAE's ambassador to the UN, announced that the Emirates would be contributing $50 million in emergency humanitarian aid for Sudan.
She said evacuation efforts would prioritise “the most vulnerable, including women and children, the sick and the elderly during the evacuations”.
“The UAE will continue providing care and accommodation assistance to the evacuees who come to our country,” she said.
“We also remain actively involved in efforts to de escalate the situation on the ground.”
Linda Thomas-Greenfield, US ambassador to the UN, said there would be “accountability for anyone”, including military political actors, who attempt to undermine or delay Sudan's democratic progress.
“The same is true for anyone who is responsible for violations of international humanitarian law and violations or abuses of human rights,” she said.
Washington's UN envoy also called “direct and indirect fire” on its diplomatic convoy and embassy “reckless and irresponsible”.