Around 40 soldiers were killed in an attack on a military base in Chad’s Lake region on Sunday, the central African country’s presidency said on Monday.
President Mahamat Idriss Deby launched an operation to track down the assailants, the statement said. It did not name the group responsible for the attack.
The Lake Chad region has been repeatedly attacked by insurgencies including by Islamic State in West Africa and Boko Haram, which erupted in northeast Nigeria in 2009 and spread to the west of Chad.
Chad is an important ally for French and U.S. forces aiming to fight jihadists in the Sahel, which has become the epicentre of global terrorism under attack by factions loyal to al Qaeda and Islamic State.
Mali, Niger and Burkina Faso have ended military operations with the U.S. and France in recent years and turned to Russia for support instead.