The aid agency Medecins Sans Frontieres (MSF) says it is pulling out of Iraq because of "escalating violence".
MSF has been present in some of Iraq's most dangerous hotspots
MSF said it had become impossible "to guarantee an acceptable level of security for our staff, be they foreign or Iraqi".
Several aid workers have been kidnapped in Iraq - including Margaret Hassan of Care International, who is still being held by her captors.
Care has stopped its operations in Iraq and appealed for Mrs Hassan's release.
MSF has 90 Iraqi staff. Its foreign workers left Iraq a month ago for Jordan.
Marc Joolen, MSF's coordinator for Iraq, said the group was considering how best to end its operation.
"It should be a matter of days," he told Reuters news agency.
An MSF statement released on Thursday said: "We deeply regret the fact that we will no longer be able to provide much needed medical help to the Iraqi people."
The group said it did not want to expose staff to the "extreme risks" run by aid workers in Iraq.
It lamented that "the warring parties [in Iraq] have repeatedly shown their disrespect for independent humanitarian assistance".
War and aid
The agency has been involved in some of Iraq's most dangerous areas, including the cities of Falluja, Najaf and Karbala.
MSF said it had also carried out 100,000 consultations this year in the Sadr City district of Baghdad alone.
MEDECINS SANS FRONTIERES
Founded in 1971 by French doctors
HQ in Brussels, offices in 18 countries
Operations in more than 80 countries
More than 2,000 expatriate volunteers, with average age of 30-35
Work includes restoring hospitals, providing vaccinations and improving sanitation and water supply
In Afghanistan, continued to work through Soviet invasion, mujahideen wars and Taleban rule
The Nobel prize-winning agency also pulled out of Afghanistan in July, after 24 years of continuous service.
It complained then that because of humanitarian works by the US, it was becoming increasingly difficult to distinguish between armed forces and aid agencies.
Five of its staff had been killed in Afghanistan. The Taleban said it carried out the attack because MSF staff were working for American interests.
Mr Joolen said the decision to leave Iraq had been taken for similar reasons.
"It's becoming increasingly difficult to operate as an
international NGO - non-governmental organisation - in a
situation ruled by the 'war on terror'," he said.