"Some troops of JEM (Justice and Equality Movement) are there in eastern Chad because troops of the government of Sudan are also there and attacked Adre," JEM commander Abdel Aziz el-Nur Ashr told Reuters.

The Chad army earlier said it repulsed an attack by Sudanese forces and rebels on Adre, a frontier town on the Chad-Sudan border, on Sunday.

Sudan denies attacking Adre and having any involvement in the Chadian conflict.

Thousands fled the Chadian capital N'Djamena after clashes between rebels and Deby loyalists and the insurgents said they were turning to face approaching JEM forces.

"We are not fighting Chadian rebels. We are fighting the government of Sudan in eastern Chad," Ashr said.

He denied any JEM troops were fighting in N'Djamena but said some Sudanese troops were there. JEM's leaders are from the same Zaghawa tribe of Deby.

Chad says Sudan is behind the latest assault on Deby's rule because it does not want a European Union force to deploy a peacekeeping force in eastern Chad to protect some 240,000 Darfuri refugees and 180,000 Chadians driven from their homes.

Khartoum denies this and accuses Chad of supporting the five-year uprising in its remolte Darfur region, where more than 200,000 people have died.