Sudan ordered at least 10 humanitarian groups expelled from Darfur on Wednesday after the International Criminal Court issued an arrest warrant for the country's president.
Secretary-General Ban Ki-moon said the action "represents a serious setback to lifesaving operations in Darfur" and urged Sudan to reverse its decision, UN deputy spokeswoman Marie Okabe said.
Aid groups protested, saying they had no connection to the court and that their absence could lead to a crisis for hundreds of thousands of war-weary Sudanese who need such basics as shelter, food and clean water.
"It is absurd that we as an independent organization are caught up in a political and judicial process," the operational director of Medecins Sans Frontieres Holland, Arjan Hehenkamp, said in a statement.
Sudan's order was announced after the International Criminal Court issued an arrest warrant for President Omar al-Bashir on charges of war crimes and crimes against humanity in Darfur.