A joint military force from Nigeria, Niger and Cameroon said on Sunday it had killed more than 100 Islamist insurgents, including 10 commanders, in the past few weeks, as it intensifies a ground and air offensive in the Lake Chad region. Boko Haram fighters and its splinter Islamic State West Africa Province (ISWAP) group have for more than a decade battled the Nigerian army in a conflict that has sucked in neighbouring states.