Many people are feared dead after an Islamist militant attack on the northeast Nigerian town of Gudumbali, two residents and a vigilante say.

Nigeria says it has negotiated the release of 82 of the more than 200 schoolgirls kidnapped by Boko Haram Islamists more than three years ago, securing their freedom in a prisoner swap deal.

A second Chibok schoolgirl abducted by Boko Haram more than two years ago has been found during military operations in northeast Nigeria, the army says.