DAKAR, Senegal (AP) — Unidentified assailants killed at least 40 soldiers during an overnight attack on a military base in the country’s west, Chad’s presidency said Monday.

President Mahamat Deby Itno visited the base in Barkaram, an island in Chad’s Lake region, early morning and announced the launch of a military operation to track the assailants, according to a statement from the presidency.

Chad has long battled with an insurgency in the country’s west, near the border with Nigeria.

It was not immediately known who was behind the latest attack, but previous attacks in the region have been blamed by the government on the Boko Haram militant group.

In March, an attack the government blamed on Boko Haram killed seven soldiers, reviving fears of violence in the Lake Chad area, after a period of peace following a successful operation launched in 2020 by the Chadian army to destroy the extremist group’s bases there. Schools, mosques and churches reopened and humanitarian organizations returned.

Boko Haram, which launched an insurgency more than a decade ago against Western education, seeks to establish Islamic law in Nigeria’s northeast. The insurgency has spread to West African neighbors including Cameroon, Niger and Chad.

Chad, a country of nearly 18 million people, has been reeling from political turmoil before and after a controversial presidential election that resulted in Deby Itno’s victory. He had led the country as interim president during the period of military rule that followed the death of his father in 2021.