U.N. Secretary-General Ban Ki-moon says Sudan's expulsion of 13 aid organizations will cause "irrevocable damage" to humanitarian operations in Darfur and is urging the government to reconsider.

Ban's spokeswoman tells reporters Thursday that the operations of the agencies "are key to maintaining a lifeline to 4.7 million Sudanese people who receive aid in Darfur."

U.N. spokeswoman Michele Montas says Ban is also concerned about the safety and security of the workers.

The International Criminal Court decided to issue an arrest warrant for Sudan's President Omar al-Bashir for war crimes and crimes against humanity.

U.N. officials said Sudan ordered the expulsion of 10 of the largest non-governmental organizations on Wednesday and three more Thursday.