New York  - The Sudanese government should allowed relief organizations to return to Darfur before a humanitarian crisis breaks out, UN Secretary General Ban Ki-moon said Thursday.

Khartoum has expelled at least 13 international relief organizations responsible for half of the humanitarian assistance in the war-torn Darfur region. More than 2 million Darfurians depended on those relief groups.

Ban said he had been urging Sudan's President Omar al-Bashir to reverse the decision to expel the relief groups, which was made last week after the International Criminal Court (ICC) issued a warrant to arrest al-Bashir after charging him with war crimes and crimes against humanity.

"We are working very hard, first of all trying to reverse this decision and not to create any humanitarian crisis so that we can continue to provide assistance," Ban said at a news conference.

"If we cannot, this may create some movement of the population, and because of the lack of sanitation and water this will create again diseases and very serious problems."

The 13 expelled groups included Oxfam, International Rescue Committee, CARE and Doctors Without Borders.

The UN said humanitarian assistance in Darfur involved Khartoum, the UN and independent relief groups, and none of which can do the work alone. dpa