Heavily armed attackers dressed as soldiers kill 400 to 500 people , witnesses say . Survivors flee to neighboring Cameroon and into the Mandara Mountains on the border . The attack is claimed by Boko Haram ( an Islamic extremist group ) who have been fighting for years against Nigeria's government in a bid to create an Islamist state across Nigeria. Insurgents destroyed mobile phone towers in the region , making communication difficult .
Heavily armed attackers dressed as soldiers kill 400 to 500 people , witnesses say . Survivors flee to neighboring Cameroon and into the Mandara Mountains on the border . Insurgents still control the area , `` and residents ca n't go back to bury the dead , '' official says . Insurgents destroyed mobile phone towers in the region , making communication difficult .