Around 40 soldiers were killed in an attack on a military base in Chad's Lake region over the weekend, the central African country's presidency said on Monday.
President Mahamat Idriss Deby was in the area on Monday to launch an operation to track down the assailants, a presidency statement said.
The presidency blamed Sunday's attack on Boko Haram in a second statement issued later on Monday. 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.