The United Nations envoy to Sudan, a key mediator in the country's brutal conflict, is no longer welcome in the African country, Sudanese authorities say.

A terse statement issued by Sudan's Foreign Ministry late Thursday comes just weeks after the head of the country's military, Gen. Abdel Fattah Burhan, demanded in a letter to envoy Volker Perthes that he should be removed from his post.

UN Secretary-General António Guterres has been notified that Perthes has been formally declared "persona non grata," the Foreign Ministry said.

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Since Apr. 15, Sudan's military, headed by Burhan, and the paramilitary Rapid Support Forces, led by Gen. Mohammed Hamdan Dagalo, have been locked in a violent power struggle that has killed more than 860 civilians, according to Sudan's Doctors' Syndicate which tracks civilian casualties. The actual death tally is likely to be much higher.

Perthes has been a key mediator in Sudan since being appointed as special envoy in 2021, first during the country's failed attempts to transition to democracy and then as relations between the military and the RSF deteriorated. Fighting exploded last month.

Neither the UN nor Volker immediately commented.

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In recent months, the German diplomat has received death threats and numerous calls to resign. In his letter last month, Burhan accused Perthes of "being partisan," and negatively contributing to pre-war talks between the generals and pro-democracy groups in the weeks building up to the conflict.

Responding to these allegations, Volker told The Associated Press that those who threatened him were marginal "extremists" and that there is a wide appreciation of UN efforts in Sudan, which has relocated its headquarters to the coastal city of Port Sudan.

The conflict between the two generals has reduced Khartoum to an urban battlefield, with many districts of the city without running water or electricity. There have been reports of widespread looting and sexual violence, including the rape of women and girls in Khartoum and the western Darfur region, which have seen some of the worst fighting in the conflict. Almost all reported cases of sexual attacks were blamed on the RSF, which didn't respond to repeated requests for comment.

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On Wednesday, 297 children were rescued from an orphanage in Sudan's capital after being trapped there while fighting raged outside, UNICEF said. The evacuation came after 71 children died from hunger and illness in the facility since mid-April.