Suspected Boko Haram jihadists killed four Chadian troops early on Monday in a newly established military outpost on Lake Chad, the military and local officials said.
Boko Haram has training camps on several of the islands that dot the vast, shallow Lake Chad, which straddles the borders of Nigeria, Niger and Cameroon as well as Chad.
"We killed 13 Boko Haram elements and we deplore the loss of four soldiers," a military source said, adding that three soldiers were injured in the attack at around 1:00 am Monday local time.
Nouki Charfadine, the governor of the Lake Chad region, also confirmed the toll.
"We set up this military post between Ngouboua and Bagassoula village after the kidnapping" of a doctor, a nurse and their driver in the area on October 31, the governor said.
Five villagers were also killed in the area in the middle of November.
The jihadist insurgency, which broke out in northeastern Nigeria a decade ago, has spilled over into neighbouring countries.
In 2015, the Lake Chad countries, together with Benin, set up a combined force to fight Boko Haram with the help of local groups of armed citizens.