Fighting has broken out again in eastern Chad between rebels and government troops.
The army has been unable to end the rebellion
It began after dawn in the town of Hadjer Meram, 100km (60 miles) from the Chad-Sudan border, sources say.
The combat is still continuing and is said to be very heavy with many dead and injured.
This latest combat comes a day after Chad accused Sudan of bombing four villages in another part of the border area on Friday.
Both the government and the rebel group involved - Union of Forces for Democracy and Development (UFDD) - claim to have the upper hand in the fighting.
Defence Minister Bichara Issa Djadallah told the BBC that the rebels are encircled, but admitted that fighting is still going on and they have not yet taken any prisoners.
Meanwhile the spokesman for UFDD, a newly formed rebel alliance, says that three government battalions have been caught in a pincer movement.
Sunday's fighting is just the latest clash in a week-long offensive by rebels in this south-eastern border region of Chad.
As well as clashes between Chadian soldiers and rebels intent on overthrowing President Idriss Deby, relations between Chad and Sudan have also deteriorated.
Earlier in the week, Chad accused Sudan of backing the rebels, and on Saturday accused Khartoum of bombing villages in eastern Chad - a charge Sudan has denied.
In April, a rebel advance reached the capital, N'Djamena, before being pushed back.