Islamist militants from Boko Haram killed 92 Chadian soldiers in an island attack in Lake Chad.
On a visit to the city, President Idriss Déby said Monday’s raid was the deadliest yet in Chad for the jihadists.
Lake Chad is the region where, for the last five years, troops from Chad, Nigeria, and Niger have been battling the insurgents in a joint campaign.
Nigeria also suffered a deadly assault Monday, when 47 soldiers were killed in an ambush from Boko Haram.
The Boko Haram rebellion started a decade ago in north-eastern Nigeria-and, according to the UN, violence has spread to neighboring countries, killing over 30 000 people and driving two million people out of their homes.
Photos showing Mr. Déby walking amid burnt-out armored vehicles on state TV in Chad.
“I’ve been involved in many operations… but we have never lost so many people in our history at one time,” Reuters news agency quoted him as saying.
The attack was on an army base on Boma Island, which lasted for seven hours, according to military sources cited by the AFP news agency.
The insurgents captured guns, who fled in speedboats along with them, they said.
Nigeria’s assault was on a convoy which had left Maiduguri’s north-eastern city carrying explosives.
The group has stepped up its attacks in recent months, following regional attempts to end Boko Haram’s campaign of terror.