Chad troops join Nigeria battle

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.

Chadian forces have also massed near the town of Diffa in Niger, Reuters news agency quotes military sources in Niger as saying.

BBC