Adre, which lies on Chad's far eastern border with Sudan's war-torn Darfur region, was attacked across the frontier by a force of 40 vehicles backed by helicopters and militiamen mounted on horseback, Chadian Colonel Osman Omer told Reuters by telephone from the town.

"The Government of Sudan attacked with both Janjaweed (militia) and helicopters. We managed to send them back in retreat all the way to el-Geneina (in Darfur)," he added.

The attack occurred as a separate force of Chadian rebels which Chad says are backed by Sudan fought with government troops loyal to Chadian President Idriss Deby in the capital N'Djamena far away to the west. Khartoum has denied it is backing the rebels.

Radio France International quoted another Chadian officer, who is the prefect of Adre, as saying that the force which attacked Adre was also backed by Russian-made Antonov planes and included rebels as well as militia.

Adre is located in Chad's violent eastern region where a European Union peacekeeping force is due to be deployed in the coming weeks with a United Nations mandate to protect thousands of Sudanese and Chadian refugees, as well as aid workers.

"The Sudanese want to disrupt the arrival of these U.N. forces in Chad, that's their objective," Adre's prefect told

RFI.

EU officials have said the fighting in N'Djamena has delayed the deployment of the European peace force.