At least 11 Chadian soldiers were killed in an attack blamed on Boko Haram jihadists at Lake Chad, the latest in a surge of attacks in the region, authorities said on Sunday.

“The Chadian army lost 11 men including three officers… and six soldiers were wounded,” the regional authority told AFP.

It added that Chadian forces killed “26 Boko Haram members” in fighting at Tchoukoutalia after the soldiers recovered cattle that the militants had seized.

Boko Haram militants have been waging a decade-long insurgency in northwest Nigeria, but the conflict has spilled into the Lake Chad region where Nigeria borders Niger, Chad and Cameroon.

Security sources earlier said seven Chadian soldiers and a guard were killed in the ambush that happened on Friday in Mbomouga in Chad’s Ngouboua area.

Since 2018, Boko Haram has carried out at least nine attacks on Chad. But the jihadist group has stepped up attacks outside Nigeria after a period of calm last year.

Last month, militants killed four people in an attack on a Cameroonian island on Lake Chad and Boko Haram killed another 13 villagers in eastern Chad.

In March jihadists killed at least 23 Chadian soldiers in an attack on an army post in the group’s deadliest attack on the country’s military.

Since 2015, troops from Cameroon, Chad, Niger and Nigeria have been grouped into a mixed, multi-national force in a bid to help fight Islamist militants.