3 February 2015 BBC Africa
Chadian troops have entered Nigeria to join the battle against militant Islamist group Boko Haram.
Armoured vehicles and infantry crossed a bridge from Cameroon following air strikes and mortar attacks on Boko Haram positions, officials say. Fighting focused on the key north-eastern town of Gamboru, Nigerian security spokesman Mike Omeri said. Chad's deepening involvement shows how the conflict with Boko Haram is taking a regional dimension. Last week, Chadian troops reportedly moved into Malumfatori, a Nigerian town which lies near the borders of Chad and Niger, after a ground and air assault against the militants.