N’DJAMENA, Chad (AP) — An explosive device detonated and killed seven soldiers in Chad during a patrol in the country’s west near Lake Chad, the government says.

The interim president, Mahamat Deby Itno, announced the deaths Monday on social media. Chadian authorities said they suspected Boko Haram extremists from Nigeria were behind the attack, renewing concerns about an escalation of violence near the border.

Boko Haram launched an insurgency more than a decade ago against Western education and seeks to establish Islamic law in Nigeria’s northeast. The insurgency has spread to West African neighbors including Cameroon, Niger and Chad. More than 36,000 people have been killed, mainly in Nigeria, according to the United Nations.

Violence has returned to 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 have reopened and humanitarian organizations have returned.

But there are concerns that a Boko Haram resurgence in Chad could affect the presidential election in May.

Deby Itno seized power after his father, who ran the country for more than three decades, was killed fighting rebels in 2021. The election is part of the country’s political transition.