A new video from Nigeria's Boko Haram extremists shows gunmen mowing down civilians lying face down, and a leader saying they are being killed because they are infidels.

The video comes two days after fleeing villagers reported that the extremists are rounding up elderly people and killing them in northeast Nigeria.

The setting of the latest video appears to be a school, a long dormitory furnished with bunk beds.

Students and schools are frequently targeted by Boko Haram, which means "Western education is sinful" in the local language.