KHARTOUM (AFP) - - The United Nations prepared on Tuesday to fly non-essential staff from Darfur as supporters of Sudan President Omar al-Beshir planned protests in Khartoum to denounce the world court prosecutor's call for him to be arrested for alleged war crimes.

On Monday, the chief prosecutor for the International Criminal Court asked for an arrest warrant against Beshir , accusing him of 10 counts of genocide, crimes against humanity and war crimes in Darfur .

The African Union-United Nations peacekeeping mission announced the staff "relocations" as Sudan promised it would do its utmost to protect peacekeepers and humanitarian workers, but said there could be no security guarantee.

Sudanese and Western officials have widely predicted that the ICC move -- seen by many in Sudan as an assault on national sovereignty -- could spark violent relatiation against Western embassies and UN peacekeepers.

"It's not an evacuation. We're temporarily relocating staff, some non-essential staff. This will probably begin today," said Josephine Guerrero, spokeswoman in Darfur for the UN-led peacekeeping mission.

"UNAMID is not pulling out. All the forces are going to be on the ground and humanitarian operations are continuing," she added, referring to the joint UN-African Union force.

A UN official, speaking on condition of anonymity, said the move, ordered by UNAMID force commander Martin Agwai, affected only about 1,800 police and 1,000 civilians who are to leave the country temporarily in coming days.

A UNAMID statement linked the move to an ambush by heavily armed militia last Tuesday in which seven peacekeepers were killed and 22 others wounded.

The Sudanese capital was bracing for angry protests against the ICC move, after Beshir's National Congress Party announced on Monday it would organise a demonstration starting at 1:00 pm (1000 GMT).

Organisers said the protest would begin at Khartoum University, go past the UNDP office, the British embassy and the UN headquarters in Khartoum.

ICC prosecutor Luis Moreno-Ocampo told journalists in The Hague on Monday that the Sudanese head of state had "personally instructed" his forces to annihilate three ethnic groups in the western Sudanese region.

"His motives were largely political. His alibi was a counter-insurgency.' His intent was genocide," he said.

It was the first time the ICC prosecutor has sought an arrest warrant for a sitting head of state and the first time it has levelled accusations of genocide.

Sudan does not recognise the ICC and refuses to hand over two other Sudanese -- including a current cabinet minister -- who face outstanding arrest warrants for alleged crimes in Darfur and said Monday's move damaged peace efforts.

In his first public appearance after the accusations were levelled, Beshir danced, punched the air in delight with his trademark walking stick and shouted 'God is Great' at an elaborate ceremony to ink the new Sudanese electoral law.

Sitting on a podium in the giant Chinese-built Friendship Hall in Khartoum before more than 500 supporters and Sudan's most senior leaders, Beshir was given roars of support as he stood to sign the landmark legislation.

The law paves the way for national elections due next year as part of a 2005 north-south peace deal in a move towards democratic transformation.

Vice President Ali Osman Taha said Sudan was in contact with the permanent members of the UN Security Council in a bid to block a formal arrest warrant. The council has the power to intervene to defer any prosecution for a year.

UN Secretary General Ban Ki-moon said in an interview with French newspaper Le Figaro that he was "very worried" by the possible fallout of any indictment of Beshir.

His office called on Khartoum to "continue to cooperate fully with the United Nations in Sudan, while fulfilling its obligation to ensure the safety and security of all United Nations personnel and property".

Darfur has been wracked by conflict since 2003. The United Nations says up to 300,000 people have died and displaced some 2.5 million from their villages.

The African Union warned the indictment of Beshir would create a power vacuum that risked "military coups and widespread anarchy".

Tanzanian Foreign Minister Bernard Membe, speaking on behalf of AU chair President Jakaya Kikwete, urged the ICC to defer bringing charges "because there is a risk of anarchy in a proportion we have not seen in this continent."

The Arab League and the Organization of the Islamic Conference have also voiced concern that Ocampo's action could undermine peace efforts in Sudan, and the United States called on all parties to stay calm.

The US government said it was bolstering security for its staff in Sudan and press secretary Dana Perino said President George W. Bush is "gravely concerned" by increasing violence in Darfur.