Boko haram militants killed at least 23 Chadian soldiers on the night leading to Friday, security sources say.
The attack is reported to be the militant group’s deadliest ever inside Chad.
The militants raided the troop’s base in the town of Dangdala, near the banks of Lake Chad.
Sources say the attackers may have crossed the border from neighbouring Niger.
Boko Haram has waged years of war in West Africa, seeking to enforce extreme jihadist principles of governance.
The war has killed tens of thousands and displaced millions others, creating humanitarian crisis in some areas.
Collective military efforts by armies from West African countries have forced the militants into hiding, though they still manage to stage attacks occasionally.
Crushing Boko haram remains a key focus for Nigerian President Muhammadu Buhari.