Following attacks by Boko Haram, many residents of Gwoza, Nigeria fled, including these people seen in this Nov. 27, 2014 photo at a refu­gee camp in Yola, Nigeria. (Sunday Alamba/AP)

A new video from Nigeria’s home-grown Boko Haram extremists shows gunmen shooting civilians lying face down in a dormitory and a leader saying they are being killed because they are “infidels” or nonbelievers.

“We have made sure the floor of this hall is turned red with blood, and this is how it is going to be in all future attacks and arrests of infidels,” the group leader says in a message. “From now, killing, slaughtering, destructions and bombing will be our religious duty anywhere we invade.”

The video released to journalists late Saturday comes two days after fleeing villagers reported that the extremists were rounding up elderly people and killing them in two schools in Gwoza, in northeast Nigeria.

The setting of the latest video appears to be a long dormitory furnished with bunk beds, which the leader says is in Bama, a town 40 miles north of Gwoza. Students and schools are frequently targeted by Boko Haram, which means “Western education is sinful” in the Hausa language.

Previously, the militants told residents of villages and towns that they would kill only enemies and that they wanted people to live peacefully in the area they have dubbed an Islamic caliphate, a large swath along Nigeria’s northeastern border with Cameroon that they have controlled for more than three months.

In the video, the leader notes that the prophet Muhammad advised that the mostly adult male prisoners should be held, not killed, but says, “We felt this is not the right time for us to keep prisoners; that is why we will continue to see that the grounds are crimsoned with the flowing blood of prisoners.”

He says some of those killed may call themselves Muslims, but they are considered infidels by Boko Haram, a Sunni Islamist militant group that imposes strict sharia law.

Thousands of people have been killed and about 1.6 million driven from their homes in the five-year insurgency, which is spilling into Cameroon, Chad and Niger.

Meanwhile, Cameroon’s army said Sunday that it had broken up a Boko Haram training camp in the Mayo-Danay district.

Lt. Col. Didier Badjeck, spokesman for Cameroon’s army, said he was traveling to the region and could not provide details until he had assessed the situation himself. The camp was dismantled Saturday.

Nigeria-based insurgents have expanded their operations in Cameroon in recent months, launching cross-border attacks as the government has become increasingly involved in regional efforts to contain them.

Jean-Pierre Mbida, a soldier with the Rapid Intervention Battalion tasked with fighting Boko Haram, said the area where the camp was discovered had been “relatively calm.”