Almost 40 people have been killed in clashes between security forces and armed raiders in eastern Chad in the past few days, the government says.
Chadian forces encounter rebels and the Janjaweed in the east
Officials say 20 civilians, eight Chadian soldiers and nine raiders were killed when Janjaweed militia attacked and partially burnt down two villages.
The government has blamed the Arab militia, based in neighbouring Sudan.
Janjaweed fighters have launched attacks from Darfur in the past year and many villages are now empty.
There have been repeated warnings that Sudan's Darfur conflict, where more than 200,000 have died and some 2m people have been displaced in three years of fighting, could spill over into Chad and the Central African Republic.
Chad's government has accused the Janjaweed of mutilating their victims.
Civilians sought refuge in the nearby refugee camp, Goz Amer, run by the United Nations refugee agency for some of the 200,000 Sudanese in Chad.
"The government response was pretty strong and there are a lot of Chadian army troops in the zone," an aid worker, who asked not to be identified, told Reuters news agency.
The head of the UNHCR, Antonio Guterres, will visit Chad on Wednesday.
The governments of Chad and Sudan accuse each other of supporting the other's rebels.
Chadian rebels launched a campaign earlier this year aimed at overthrowing President Idriss Deby.
The UN says about 90,000 Chadians have been displaced by recent fighting.