Boko Haram fighters are overrunning villages near the Nigerian town of Chibok, forcing hundreds of people to flee as they loot and burn in the area, local leaders have said.

Nigeria’s military launched a co-ordinated air, naval and ground assault to free 19 hostages held in militant camps in the oil-rich southern delta, apparently routing the gunmen without causing any casualties.

An opposition bloc called for Nigerians to mount peaceful protests to demand cancellation of a "sham" presidential vote in which the governing party was declared the winner.