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 ISIL in West Africa and Boko Haram, which erupted in northeast Nigeria in 2009 and spread to the west of Chad, Reuters news agency reported.
Chad is an important ally for French and US forces aiming to fight jihadists in the Sahel, which has become the epicenter of global terrorism under attack by factions loyal to al Qaeda and ISIL.
Mali, Niger and Burkina Faso have ended military operations with the US and France in recent years and turned to Russian for support instead.
MA/PR