Nigerian forces invade last known stronghold of Boko Haram

BAUCHI, Nigeria (Reuters) - Nigerian forces backed by warplanes invaded Islamist group Boko Haram's last known stronghold, the Sambisa forest, on Wednesday, in an effort to finally defeat their six-year-old insurgency, two military sources said.

Armies from Nigeria and neighbours Chad, Niger and Cameroon have in the past two months launched a concerted push to try to crush the insurgents, who have killed thousands and kidnapped hundreds in their battle to establish an Islamic state.