The International Red Cross has suspended operations in Baghdad after a Canadian member of the humanitarian team was killed in the capital.
The ICRC has urged all soldiers to grant its vehicles safe passage
Vatche Arslanian, 48, was travelling in a Red Cross vehicle when it was hit by gunfire on Tuesday.
The International Committee of the Red Cross (ICRC) responded on Wednesday by halting work in Baghdad, saying staff movement now involved "incalculable risks".
The body of Arslanian, who was in charge of logistics in Iraq, was found later on Wednesday.
The ICRC is deeply distressed by its inability to rescue its staff member
"We have managed to recover the body. He was caught in crossfire. It was not a targeted hit on our car. There was
fighting," said ICRC spokeswoman Nada Doumani.
She said 12 other people were believed to have died in the
incident, when a number of vehicles were trapped in fighting.
Other workers in two Red Cross vehicles managed to escape.
An ICRC statement issued after Arslanian went missing read: "The ICRC is deeply distressed by its inability to rescue its staff member and by its temporary inability to pursue its emergency assistance to those in need."
The agency said the two vehicles were clearly marked with red crosses.
ICRC spokesman in Baghdad, Roland Huguenin-Benjamin, said ambulances were unable to retrieve casualties in many
parts of the city.
"There are lots of situations in which casualties have been seen and there was no possibility of evacuating them... there was immediate fire as soon as anybody tried to approach."
Baghdad's hospitals are being overwhelmed with new patients
The ICRC has six international employees in Baghdad along with local staff.
The team in Baghdad would continue to assess the situation and would resume its activities if and when possible, it said.
The organisation called on all soldiers to grant safe passage to Red Cross and Red Crescent vehicles.
The decision to halt operations comes as a second international relief group working in Baghdad, Medecins Sans Frontieres (MSF), suspended work after two of its staff members vanished in the capital.
MSF's head of mission in the city, 43-year-old Frenchman François Calas, and Ibrahim Younis, a 31-year-old logistician of Sudanese descent, were last seen on Wednesday.
Hospitals in Baghdad have been overwhelmed by patients and are running out of medicine, water and electricity.
Casualties have been admitted on an average of 100 per hour, with staff working day and night.