By Opheera McDoom

KHARTOUM, July 11 (Reuters) - International organisations in Sudan tightened security on Friday, fearing a violent backlash if the International Criminal Court seeks an arrest warrant for President Omar Hassan al-Bashir as expected on Monday.

ICC Prosecutor Luis Moreno-Ocampo is due to submit to the judges "evidence on crimes committed in the whole of Darfur over the last five years" and seek to charge an individual or individuals, a prosecution statement said on Thursday.

It gave no details. The Washington Post quoted U.N. officials and diplomats as saying the ICC prosecutor would charge Bashir with genocide and crimes against humanity on Monday.

"In light of recent security developments staff are advised to upgrade their personal security measures," an urgent security notice sent to U.N. staff in Khartoum obtained by Reuters said.

The notice told staff to refrain from all but essential movement over the weekend and after dark.

"Ensure that you have an adequate supply of food and water in your home for several days, and that your vehicle is fully fuelled. Keep your personal documents and other essentials available," it said.

The U.S. State Department withdrew all staff from the war-torn western region of Darfur, including those working for its humanitarian arm USAID, aid workers said.

U.N. agencies there were practising evacuation drills and might pull out all but essential staff, they added.

The U.N. mission in Sudan and the U.S. embassy all declined to comment officially on security preparations.

AMBUSH BY MILITIA

After ICC-prompted warrants for the arrest of two Sudanese suspects last year, there were government-organised protests in Khartoum's streets, while in Darfur, the world's largest humanitarian operation is already badly hampered by insecurity.

Seven people were killed on July 8 in an ambush by militia of joint U.N.-African Union peacekeepers in Darfur. One militia leader has already been indicted by the ICC.

Khartoum refused to hand over the militia leader and another indicted person, former state Minister of the Interior Ahmed Haroun. Instead, it made Haroun state minister of humanitarian affairs.

International experts estimate about 200,000 people have died and 2.5 million have been driven from their homes since mostly non-Arab rebels took up arms in early 2003, accusing the central government of neglect.

Khartoum mobilised mostly Arab militia to quell the revolt. They stand accused of systematic rape, looting and murder.

A warrant for Bashir, which would have to be approved by the ICC judges, will make international travel for the head of state practically impossible and render high-level diplomatic contact difficult.

Interpol arrest warrants placed with key Western regional allies could stop Bashir, a Muslim, travelling even on the pilgrimage in Saudi Arabia. The ICC said they had tried to divert a plane carrying Haroun on the pilgrimage this year.

Julie Flint, author of a book on Darfur, said there was no reason to believe the government would not react as viciously to the latest challenge to its survival as it had to earlier ones.

She and others were concerned at the timing of the ICC announcement before Sudan's first democratic vote in 23 years, due in the first half of 2009.

"If Bashir is brought to court and convicted, it will be a blow against impunity," she said. "If he remains in power, unreformed and unrepentant despite indictment by the ICC, it risks being a blow for impunity," she said. (For the latest humanitarian news visit Reuters AlertNet http://www.alertnet.org) (Editing by Philippa Fletcher)

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