Nigerian forces backed by war planes invaded Islamist group Boko Haram's last known stronghold of 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.
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