The UN secretary general has urged Sudan to rethink its decision to expel aid groups from its Darfur region.
Ban Ki-moon said the decision could cause "irrevocable damage" to the humanitarian operations in Sudan.
The order came after the International Criminal Court (ICC) issued an arrest warrant for Sudanese President Omar al-Bashir over alleged war crimes.
Aid agencies have expressed concern over the potential impact of the move on thousands of displaced people.
The African Union and Arab League have said they will ask the UN to defer the warrant for a year, saying that arresting Mr Bashir could derail attempts to bring stability to Sudan.
A statement from Mr Ban's office said the decision to expel 13 non-governmental organisations "will, if implemented, cause irrevocable damage to humanitarian operations there".
"The operations of these agencies are key to maintaining a lifeline to 4.7m Sudanese people who receive aid in Darfur," it said.
The statement also expressed concern about the safety and security of national and international humanitarian workers in Sudan and their assets.
"The confiscation of equipment, money and other materials is unacceptable and must end immediately," it said, while stressing that the agencies involved affected had acted "in a neutral and impartial manner".
