Updated

The U.N. security coordinator is being asked to step aside while an independent team assesses security failures that led to so many casualties in a bombing at U.N. headquarters in Baghdad (search), U.N. officials said Monday.

Secretary-General Kofi Annan (search) is expected to appoint the team of experts on Tuesday. Tun Myat (search) of Myanmar (search), who has been security chief since July 2002, will go on leave at least until their assessment is completed, the officials said, speaking on condition of anonymity.

In a letter to over 25,000 U.N. staffers worldwide on Friday, Annan said he planned to appoint the team and pledged to take immediate action to implement recommendations in a highly critical report by a U.N.-appointed panel.

The report blamed "dysfunctional" U.N. security for unnecessary casualties in the Aug. 19 attack that killed 22 people, including top U.N. envoy Sergio Vieira de Mello, and injured more than 150 others.

Annan told the staff he was reviewing "the serious weaknesses" in the management of the U.N. security system, as well as the threats facing U.N. missions worldwide.

Annan said Monday that he plans to make security changes this week. Annan stressed that U.N. security will be tightened worldwide.

Last week, Annan ordered the temporary withdrawal of the U.N.'s international staff from Baghdad for consultations with a team from U.N. headquarters following an upsurge in attacks. Fewer than 20 foreign staff were still in the Iraqi capital.