UN Special Representative in Sudan Volker Perthes. Photo courtesy of UN official website
Khartoum in June declared Perthes persona non grata and accused him of bias after he denounced possible "crimes against humanity" in the conflict.
Perthes had been the UN representative to Sudan for more than two years, heading up the UNITAMS mission that was created in 2020 after the ouster of former leader Omar al-Bashir.
"I am grateful to the Secretary-General for that opportunity and for his confidence in me, but I have asked him to relieve me of this duty," Perthes told the UN Security Council.
"This will therefore be my last briefing in this function."
United Nations chief Antonio Guterres said Perthes' resignation was accepted, adding "he has very strong reasons."
Perthes warned again Wednesday that the conflict between forces under General Abdel Fattah al-Burhan and the paramilitary Rapid Support Forces (RSF) of General Mohamed Hamdan Daglo is in danger of further deterioration.
"What started as a conflict between two military formations could be morphing into a full-scale civil war," he said, as "the fighting shows no sign of abating while neither side appears close to a decisive military victory."
"We need to impress on the warring parties that they cannot operate with impunity, and there will be accountability for the crimes committed," he added.
Last month, when Perthes did not show up to a UN briefing on the conflict, the United States accused Sudan of having threatened to expel the UN mission, with ambassador Linda Thomas-Greenfield claiming Khartoum had vowed to end the mission if Perthes participated.
The Sudanese ambassador denied the claim.
Earlier Wednesday, a medical source told AFP that at least 40 civilians had been killed in an air-raid that hit two markets and neighborhood areas in the western region of Darfur, which has seen some of the worst fighting of the war.
Since April 15, nearly 7,500 people have been killed, according to a conservative estimate from the Armed Conflict Location & Event Data Project.