By Opheera McDoom

KHARTOUM, July 15 (Reuters) - The United Nations urged hundreds of its staff to stay at home on Tuesday as thousands of Sudanese prepared to protest against war crimes charges levelled against their president by an international court.

The International Criminal Court's (ICC) Chief Prosecutor on Monday asked judges to grant an arrest warrant for President Omar Hassan al-Bashir for genocide, war crimes and crimes against humanity in Darfur.

Protests so far have been staged by pro-government bodies but even Sudanese who traditionally oppose Bashir have backed him against the Hague-based ICC.

Demonstrators hung pictures of Bashir on the walls of the U.N. headquarters in Khartoum and the British embassy.

U.N. security officials told non-essential staff to stay at home on Tuesday ahead of Tuesday's expected protests.

A group was formed on the social networking site Facebook to support Bashir after the ICC announcement and within a few hours it had attracted almost 1,000 Sudanese at home and abroad.

"I am someone who doesn't agree with Bashir and the way he runs the country ... but when there is a challenge to the nation and its sovereignty, it's another issue," the group's creator wrote.

"A beast may kill one revolutionary but the earth will bear forth a thousand more," Ahmed Hashim Ibrahim added.

Sudan's government has reassured international workers it will ensure their safety, but the United Nations raised security levels in Khartoum and Darfur ahead of the Hague court's announcement, fearing a violent backlash.

Families have been evacuated from Khartoum and non-essential staff moved out of Darfur.

Many aid agencies said they had pulled staff from rural areas back to towns in Darfur. The United Nations declined to comment on how its huge humanitarian operation in Sudan's west would be affected by the security measures.

The joint U.N.-African Union peacekeeping mission, or UNAMID, said it would also begin relocating some non-essential staff, although core operations would continue.

"We are looking at a trend of security in the past couple of months and the ICC could be another aspect we are looking at but it's not the only reason the UNAMID security level has been raised," said spokeswoman Josephine Guerrero. (Editing by Giles Elgood)

AlertNet news is provided by