The UN says that attacks on aid workers in eastern Chad have doubled since last year [EPA]
Elisabeth Byrs, a UN spokeswoman, said on Friday that the aid groups include the international Red Cross and French group Doctors Without Borders.
The UN says that six aid organisations have halted their work in Chad because of the risk of their staff being abducted or killed.
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.
in Chad in Chad
Six aid groups have suspended work in Chad today after the killing of one aid worker, a rash of banditry, and a kidnapping, according to the United Nations. The UN says about 37,000 people will be affected in some way by the move.

UN spokeswoman Elisabeth Byrs noted that the  and '''' (Doctors Without Borders) are among those to halt operations. "To date, five NGOs non-governmental organisations and the ICRC International Committee of the Red Cross have temporarily suspended their activities in the east," Byrs said. "Serious acts of banditry in eastern Chad over the last two weeks jeopardise the continuity of humanitarian operations."

This comes soon after a worker for the Red Cross, Laurent Maurice, was kidnapped earlier in the week and another local aid worker for the ''Solidarités'' agency was killed.

Over fifty attacks on humanitarian aid workers in Chad have been made this year by bandits. Relief workers are targeted by criminals because they have valuables and vehicles.