* Darfur faces deeper crisis a month after expulsions
* More aid groups needed to fill gap
* US envoy to help with peace efforts
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By Andrew Heavens
KHARTOUM, April 4 (Reuters) - Darfur is on the brink of a deeper humanitarian crisis following Khartoum's expulsion of aid groups and needs a new relief push within weeks, the U.S. special envoy to Sudan said on Saturday.
Envoy Scott Gration spoke as he travelled through north Darfur a month after Sudan expelled 13 foreign aid groups and closed three local organisations it accused of helping build a war crimes case against the country's president.
He told reporters by phone he had just visited Zamzam refugee camp, where buildings run by the ousted aid groups remain closed, health services were hit and water reserves were close to running dry.
"I was very concerned with what I saw. We are on the brink of a deeper crisis in Darfur," Gration said.
"We have to increase the capacity and number of aid agencies that are able to move aid assistance from the warehouses to the distribution points and then to the hands and mouths of the people in these camps."
It was his first visit since U.S. President Barack Obama named the retired Air Force general last month as special envoy to war-ravaged Sudan.
President Omar Hassan al-Bashir accused the expelled aid groups and local organsiations of passing information to the international Criminal Court, which issued an arrest warrant against him on March 4 on charges of war crimes in Darfur.
The groups, including Oxfam, Save the Children and Medecins Sans Frontieres, deny working with the court and the expulsions have drawn international condemnation.
International experts say at least 200,000 people have died and more than 2.7 million have been driven from their homes in almost six years of ethnic and politically driven fighting in Darfur. Khartoum says 10,000 people have died.
Gration said Sudan needed to fill the gap left by the expelled groups by bringing in new organisations from Arab countries and the west and by building up local groups. He called on Khartoum to return about 400 vehicles and other seized assets and to speed up visa applications for new aid workers.
"I don't think that the prospects for returning the 13 NGOs ...are very strong or very high," he said.
Gration will travel to Qatar at the end of April to meet the U.N. and African Union's Darfur mediator, Djibril Bassole.
Darfur's rebel Justice and Equality Movement last month suspended its participation in tentative talks with Sudan's government in Doha, protesting against the aid expulsions.
Sudan says it plans to replace the expelled organisations with other international groups and Sudanese humanitarian operations. Bashir has also said he wants Sudanese groups to handle all the delivery of aid.
The expulsions hit aid programs across North Sudan, and the United Nations has said that, beyond Darfur, there are also particular worries on the impact on Abyei, Southern Kordofan and Blue Nile -- three oil-rich regions along Sudan's contested north-south border.