In northern Iraq UN workers will, however, remain.
"We have asked our staff in Baghdad to come out temporarily for consultations with a team from headquarters on the future of our operations, in particular security arrangements that we would need to take to operate in Iraq," UN spokeswoman Marie Okabe said late on Wednesday in New York.
Okabe would not say when the staff would leave Baghdad or give other details. UN officials, speaking on condition of anonymity, said about 20 UN staff members remained in Baghdad and about 40 others across Iraq.
UN Secretary-General, Kofi Annan, in late September ordered all but a skeleton UN staff needed for essential services to leave the country, following two bombings at the world body's headquarters in Baghdad.
US troops raid homes desperate to get
at resistance fighters
The latest UN decision was announced two days after a deadly car bombing at the Baghdad headquarters of the Red Cross.
The International Committee of the Red Cross and the humanitarian group Medecins Sans Frontieres, or Doctors Without Borders, also said on Wednesday they were pulling out workers, despite pleas from the US administration to stay.
The Red Cross said it would remain in Iraq, but would reduce the number of international staff - now about 30 - and increase security for those who stay. The agency has 600 Iraqi employees.
Meanwhile, US troops have fanned out across downtown Tikrit in pre-dawn raids and detained several people, believed to be setting up a new resistance unit in Saddam Hussein's hometown.
In Tikrit, raids of six houses on Wednesday followed "reliable intelligence" that the suspects were helping to establish a new network to attack US-led troops, Lt Col Steve Russell said.
Four people were detained and 10 others were taken in for questioning, Russell said. Occupation troops discovered false identification cards and multiple fake license plates with "official government stickers" in one of the houses.
"We have asked our staff in Baghdad to come out temporarily for consultations"
The 10 were arrested, interrogated, handcuffed, blindfolded and then taken away in trucks, witnesses told our correspondent.
"We continue to work against these cells, to disrupt, capture or kill them," Russell said.
Our correspondent quoting witnesses reported that in another raid early on Thursday, US forces, backed by armoured vehicles, raided a house in the Abu Ghuraib area of west Baghdad and arrested 10 of its residents.
US forces found weapons and rocket-propelled grenades in the searched house, the witnesses said.
In a fresh resistance attack, two US military camps, Kafar Qassim camp and another one in al-Qala area, near Samarra, came under separate mortar attacks on Thursday, our correspondent reported.