Chad's government announced a state of emergency late Monday in the Lake Chad region where Islamic extremists from neighboring Nigeria have launched several attacks in the past few months.

Nigeria-based Boko Haram militants have been stepping up attacks in Chad, Niger and Cameroon after those countries agreed to help fight the extremists.

Investigators say Boko Haram terrorists abducted hundreds of schoolgirls last year and used them as sex slaves. Most of the girls remain kidnapped.

Chad's government announced on national radio that movements of people and vehicles will be restricted so that authorities can search homes and collect weapons during the day and night to prevent attacks around the lake region.

Over the weekend, two girls wearing suicide vests detonated explosives in Ngouboua village along Lake Chad killing two people, according to national radio. Five coordinated suicide bombings in October killed at least 36 people in Baga Sola near Lake Chad.