Medecins Sans Frontieres accused coalition forces in Iraq of breaking humanitarian laws as it closed its mission last week because of the escalating violence.
In a statement, the general director of MSF in Belgium, Gorik Ooms, attacked both sides in Iraq for showing "disrespect for independent humanitarian assistance".
A spokeswoman added: "There has been a closing of humanitarian space in Iraq. Coalition forces have entered hospitals armed, and blocked access, which is contrary to humanitarian law."
She said these incidents were concentrated in Falluja and Karbala. MSF had 90 national staff and a handful of international staff in Iraq. The foreign aid workers had already been evacuated to Oman.
MSF's departure follows those of the Red Cross, Care International, Oxfam and Save the Children.