Western aid groups say they have evacuated more than 250 aid workers from Sudan's troubled Darfur region because of new security fears.
British group Oxfam said Friday that workers have seen increasing military activity, banditry and direct violence on aid workers in Darfur this month.
It said nearly half a million people in the area have less access to humanitarian aid because of the violence.
The affected aid workers are from Oxfam and several other groups - Concern Worldwide, Goal, International Rescue Committee, Norwegian Refugee Council and World Vision.
Also Friday, Oxfam said a wave of violence in eastern Chad has forced aid groups to evacuate 400 humanitarian workers from that area.
Chad's military has been battling rebel forces near the border with Sudan. Also, the United Nations has reported attacks on villages in the area by Arab militias.
Aid officials say the evacuations in Chad threaten to cut needed assistance to thousands of displaced Chadians and Sudanese refugees.
Some information for this report was provided by AFP.