"The government of the Republic of Sudan has notified the secretary-general of the United Nations that it has declared Mr. Volker Perthes... persona non grata as of today," the foreign ministry said in a statement late Thursday.
A Sudan government official who spoke to AFP on condition of anonymity said the decision was taken "because he sided with certain political parties and stressed that the political process be restricted to certain parties and exclude others."
"When the head of the sovereign council (Gen. Abdel Fattah al-Burhan) wrote to the U.N. secretary-general asking for him to be replaced, and he did not respond, the Sudanese government had no choice but to take this decision," the official added.
In a letter to the United Nations last month, al-Burhan accused the envoy of bias, not respecting "national sovereignty" and exacerbating fighting between the regular army he leads and the Rapid Support Forces led by Gen. Mohamed Dagalo.
U.N. chief Antonio Guterres has repeatedly defended Perthes.
Fighting has raged in the northeast African country since mid-April, when al-Burhan and his former deputy Dagalo turned on each other.
The United Nations noted in a tweet on Thursday that Perthes was in the Ethiopian capital Addis Ababa for a series of talks.