Boko Haram Islamist militants have killed 92 Chadian soldiers in attack on an island in Lake Chad.
President Idriss Déby said on a visit to the area that Monday's raid was the jihadists' deadliest yet in Chad.
Lake Chad is the region where forces from Chad, Nigeria and Niger have been fighting the insurgents in a joint campaign for the last five years.
Nigeria also experienced a deadly attack on Monday, when 47 soldiers were killed in a Boko Haram ambush.
The Boko Haram insurgency began in north-eastern Nigeria a decade ago - and the violence has spread to neighbouring countries, killing more than 30,000 people and forcing two million from their homes, according to the UN.
