Chad launched a US-backed counter-terrorism exercise on Monday grouping 1,300 soldiers from 28 African and Western countries, billing it as a warm-up for an offensive against Nigerian Islamist insurgent group Boko Haram. The "Flintlock" maneuvers unfold as Chad and four neighbouring states prepare a taskforce to take on Boko Haram, the biggest security threat to Africa's top energy producer Nigeria and an increasing concern to countries bordering it.