Relations between the two countries have deteriorated in recent weeks despite both nations signing a reconciliation agreement in Doha, the capital of Qatar.

Tense relations

Chad two weeks ago accused Sudan of backing an assault by the Union of Resistance Forces (UFR).

The attack was repelled and more than 200 rebels killed, but Chad carried out air raids against retreating rebels on Sudanese soil, which Sudan called an "act of war".

The rival neighbours have long accused each other of conducting proxy wars through rebel groups, and only resumed diplomatic ties in November after cutting them in May 2008.

Chadian rebels have been attempting to topple President Idriss Deby for the last few years.

Sudan faces its own rebel movement in the restive Darfur province, and last year accused Chad of backing rebels who launched an attack on Khartoum.

Good relations between Chad and Sudan are seen as a crucial to peace to Darfur, where the United Nations says up to 300,000 people have died in six years of conflict.