The International Committee of the Red Cross (ICRC) has said it will reduce its foreign staff in Iraq, after its headquarters in Baghdad was bombed on Monday.
Red Cross staff will choose whether to stay or leave
The agency, which has about 30 international and 600 Iraqi staff in Iraq, stressed it was not pulling out of the country.
Two ICRC workers were among more than three dozen people killed in a series of co-ordinated suicide attacks in the Iraqi capital.
On Tuesday, US Secretary of State Colin Powell personally appealed to the head of the ICRC not to withdraw its foreign staff from Iraq.
The ICRC's decision to scale back came a day after medical charity Medecins Sans Frontieres said it would pull out four of its seven expatriate staff in Iraq following the Red Cross attack.
Other aid agencies and non-governmental organisations reduced their staffing levels in Iraq, or pulled out entirely, after the UN headquarters in Baghdad was bombed in August, killing at least 20 people.
The announcement came amid continuing violence in Iraq, with the deaths of two US soldiers killed by a roadside bomb 40 kilometres (25 miles) north-east of Balad, 75 km (45 miles) north of Baghdad, on Tuesday.
It brings the number of US soldiers killed in Iraq since the end of the war on 1 May to 115, exceeding for the first time the toll of troops killed during major combat.
A US research group, meanwhile, has said about 13,000 Iraqis, including as many as 4,300 civilians, were killed during the war.
The Project on Defense Alternatives (PDA) said that despite the advent of precision weapons, more civilians probably died in the latest conflict than in the 1991 Gulf War.
"The ICRC is not withdrawing from Iraq," said Pierre Kraehenbuehl, the agency's director of operations.
"We are reducing the number of our international staff and increasing measures for the security of the remaining staff," he said.
He said the terms of the Geneva Convention on the protection of civilians in times of war meant it was incumbent on the ICRC to stay in Iraq while the country was occupied.
But he said the staff's safety was a priority and any foreign or Iraqi ICRC workers will be asked whether they want to stay or leave.
Florian Vestphal, an ICRC spokesman in Geneva, told the BBC's Newshour programme the agency will take additional measures to enhance the safety of its staff in Iraq.
"[But] what is obvious is that in this kind of situation we simply cannot guarantee 100% protection," he said.
He said the withdrawal of staff will impact on the agency's work, but the ICRC "still think that even under these extremely difficult circumstances there is a role we can play".
The BBC's Jill McGivering in Baghdad says the news may be greeted with dismay as yet another sign of falling confidence.
The ICRC has an essential role to play in Iraq while the country is under occupation, our correspondent adds.
One of its main functions is monitoring the treatment of detainees, acting as an independent watchdog to make sure the coalition does not violate international humanitarian law.
Other tasks, our correspondent says, include supplying equipment and medicines to hospitals, helping hospitals with basic repairs and tracing missing people - all vital at a time of instability and conflict.