The UN says that six aid organisations have halted their work in Chad because of the risk of their staff being abducted or killed.
Elisabeth Byrs, a UN spokeswoman, said on Friday that the aid groups include the international Red Cross and French group Doctors Without Borders.
The announcement comes after Laurent Maurice, a Red Cross worker, was kidnapped on Monday and a Chadian aid worker was recently killed.
According to a source close to the international peacekeeping force in the reigion, Maurice's kidnappers have demanded $1.5 million for his release.
Several armed men on Monday seized the French worker who was in eastern Chad to assess recent harvests in the village of Kawa, about 10km from the border with Sudan.
General Oki Dagache, who heads co-ordination with the international force in eastern Chad, has blamed the kidnapping on "crooks from Sudan" and said the kidnappers had crossed back into Sudan's western Darfur region with their captive.
Byrs said the suspension leaves at least 37,000 people without aid and that attacks on aid workers in eastern Chad have doubled to about 190 compared with last year.
At least 70 United Nations and other aid organisations provide food, water, and medical help to more than 250,000 Sudanese refugees and uprooted Chadians in the east.