KHARTOUM - The humanitarian situation in Darfur remains precarious after the Sudanese government's decision to expel 13 international aid agencies, the United Nations said Tuesday.

It warned it would have to appeal to international donors for extra funds beyond the 2.18 billion dollars it has already requested in order to meet the needs going unmet as a result of the expulsion of the agencies' 3,142 staff.

"The most critical needs are being filled for now," UN humanitarian affairs coordinator Ameerah Haq said here, explaining that food rations for the months of March and April had already been distributed to some 1.1 million of the people in greatest need in Darfur.

"However, by the beginning of May, as the hunger gap approaches, and unless the World Food Programme has found partners able to take on the mammoth distribution task, these people will not receive their rations," she said.

"Up to 650,000 currently do not have access to full health care," she added.

At UN headquarters in New York, UN humanitarian chief John Holmes said that despite a "significant effort" by the Khartoum government, the UN and remaining aid groups to plug some of the immediate gaps, "these are band-aid solutions... not long-term solutions."

He singled out gaps in food aid; health and nutrition; non-food items and shelter; and water, sanitation and hygiene upon which some 4.7 million Darfur people depend for survival.

He described the joint UN-Sudan assessement of the humanitarian situation in Darfur "a good step forward" but "only the first of many steps."

UN officials said the expulsion of the 13 key non-governmental organizations (NGOs) had led to a loss of expertise in technical assessments, planning, program design and implementation, monitoring and evaluation.

And they noted that such capacity could not be replaced easily or quickly.

Haq for her part said that urgent steps need to be taken now to start prepositioning food and shelter ahead of the rainy season to cater for the estimated 2.7 million people who have fled their homes as a result of the six-year-old conflict.

She added that the expulsion of the foreign relief staff by Khartoum in response to an international arrest warrant for war crimes issued against President Omar al-Beshir would force UN agencies to recruit additional personnel of their own to meet the shortfall.

"WFP has taken on the national staff themselves ... UNICEF will have to bring more people ... So we need to bring in more staff."

She warned that was bound to have an impact on the costs of the UN relief operation.

"So absolutely the operating cost for the UN agencies is going to go up... Clearly it will rise."

"Prevailing bureaucratic impediments should be lifted and security conditions should not complicate issues such as access, if the people of Darfur are not to end up facing the most serious upheaval in years," Haq noted.