The U.N. said Thursday it has temporarily pulled international staff out of parts of Somalia controlled by Islamic radicals after receiving written threats.

The U.N. said the threats came shortly after the Sept. 17 shooting deaths of an Italian nun and her bodyguard in the capital, Mogadishu, which was seized by an Islamic militia in June. Somalia's president narrowly escaped a suicide car bombing a day later in Baidoa, the seat of the weak U.N.-backed government.

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"Given the insecure environment and the subsequent direct written threats against U.N. staff, a decision was taken to temporarily relocate all U.N. international staff members from southern and central Somalia," the U.N. said in its monthly review of the situation in Somalia.

It added that it has suspended "all U.N. missions to Mogadishu until further notice."

The review did not give details of the threats or say when it pulled out its staff. A U.N. official, who spoke on condition of anonymity because he was not authorized to speak to the media, said the threats came from Islamic extremists.

The U.N. said it was assessing the security situation in the war-ravaged country to decide when its international workers should return. It said it was still carrying out humanitarian work through Somali staff. Somalia is facing a humanitarian crisis, with 1.8 million Somalis in need of aid because of drought.

The U.N. also pulled staff members from Puntland , a semiautonomous region not controlled by Islamic forces, but they have since returned, the review said.

Somalia has not had an effective national government since 1991, when warlords overthrew dictator Mohammed Siad Barre and then turned on one another, throwing the country into anarchy.

A transitional government was formed in 2004 with U.N. help, but it has struggled to assert authority.

The Islamic movement controls much of Somalia's south. Its strict interpretation of Islam has raised fears of rule like that of Afghanistan's ousted Taliban regime.

The United States has accused the group of sheltering suspects in the 1998 Al Qaeda bombings of U.S. embassies in Kenya and Tanzania. Bin Laden has said Somalia is a battleground in his war on the West.