"There were clashes today," FUC rebel spokesman, Abdoulaye Abdelkarim, told Reuters
He said a force of more than 2,000 fighters led by his brother, Mahamat Nour, who heads a military faction of the rebel United Front for Democratic Change (FUC), was on the move in the Guereda region in eastern Chad, which borders with Sudan.
"The objective is to head towards N'Djamena," he added, referring to the Chadian capital which lies some 700 km (440 miles) to the west of the latest reported fighting.
Government military officers in N'Djamena, who asked not to be named, said clashes between government forces and rebels had taken place at Aram Kolle, 65 km (40 miles) east of the town of Biltine.
"Government forces are in control of the situation," one officer said. Neither side gave details of casualties.