Chad's defense minister has claimed victory in a fierce battle fought with rebels near the Sudanese border.
Bichara Issa Djadallah said government forces had killed at least 100 rebels in Sunday's fighting.
The fighting came days after President Deby's government accused Sudan of bombing four towns along its eastern frontier. Sudan denied the accusations.
The two oil-producing central African nations accuse each other of supporting rebels hostile to the other's government.
Sudan and Chad cut ties earlier this year after Chadian rebels launched an attack on the Chadian capital, Ndjamena, aimed at unseating President Deby.
The new violence raises concerns about an August peace deal signed by the two nations in an effort to improve ties and end hostilities.
The United Nations announced last week that it was sending peacekeepers to Chad and the neighboring Central African Republic to look for ways to protect refugees from violence linked to the conflict in Sudan's Darfur region.
The world body says eastern Chad is now home to more than 200,000 Darfur refugees and 50,000 internally displaced Chadians.
Some information for this report was provided by AFP and Reuters.