The Sudanese government has declared the UN envoy to the country, Volker Perthes, to be "persona non grata", meaning it no longer recognises his position in Sudan.
"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 Ministry of Foreign Affairs said in a statement on Thursday.
Mr Perthes was in Addis Ababa, Ethiopia, on Thursday for a series of diplomatic talks, according to the UN mission's Twitter feed.
The head of the Sudanese armed forces - and Sudan's de facto leader - General Abdel Fattah al-Burhan, recently accused Mr Perthes of stoking the country's conflict.
He demanded he be replaced.
Before the start in April of the conflict between the army and its paramilitary rival, the Rapid Support Forces, the UN mission in Sudan had been targeted by protests denouncing alleged foreign interference.