0703 GMT September 18, 2021
Seventeen attackers also died in the clash in an area that has seen a series of raids by the fighters, increasingly moving out of their heartlands to strike in Nigeria's neighbors, Reuters reported.
Chad is a leading contributor to an 8,700-strong regional force fighting Boko Haram terrorists, a terrorist group that wants to carve out a state and has allied itself to ISIL.
"It was around 4 a.m. that they attacked us by surprise," an officer involved in the battle in the Lake Chad border region said.
Chad's President Idriss Deby has said he believes Boko Haram can be defeated by the end of the year.
His capital N'Djamena is less than 100km (60 miles) from the group's stronghold in northeastern Nigeria and will be the regional force's headquarters.