DAKAR, Senegal (AP) — Chad’s presidency said at least 40 soldiers were killed by unidentified assailants during a Sunday night attack on a military base in the country’s west.

President Mahamat Deby Itno visited the base early Monday morning and announced the launch of a military operation to track the assailants.

Chad has long battled with an insurgency in the country’s west, near the border with Nigeria. In June nine people were killed and more than 40 injured when a fire set off explosions at a military ammunition depot in the capital, N’Djamena.

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.