Fiona Terry, director of research with Medicins sans Frontieres in Paris, said international relief NGOs sometimes do more harm than good.
Terry, in London to discuss her new book, Condemned to repeat: the paradox of humanitarian action, said: "Aid organisations don't look at the ethics of humanitarian action. They are just concerned with the technical questions of providing aid."
The book examines the way in which NGOs provided aid to Rwandan refugee camps in Zaire and Tanzania from 1994-96.
"In Rwanda, aid allowed the ex-FAR (the former Rwandan military responsible for the genocide) to rearm. If aid is turned against the people it is intended to help, agencies should get out," said Terry.
She said some agencies were reluctant to withdraw from countries for fear of losing funding.