The Nigerian terrorist group Boko Haram has released a video online on Saturday that showed gunmen shooting down civilians lying face down in a dorm, with a leader justifying the killing because they are all "infidels" or non-believers.

According to Haruna Umar of the Associated Press, many of the victims appear to be adult men. So many people died in the video that the gunmen are seen having difficulty trying to ensure that everyone remained dead.

"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 said in a message. "From now, killing, slaughtering, destructions and bombing will be our religious duty anywhere we invade."

The Associated Press added that the video was released two days after fleeing villagers in northeast Nigeria reported extremists rounding up elderly people and executing them in two schools there.

"The setting of the latest video appears to be a school, a long dormitory furnished with bunk beds which the leader says is in Bama, a town 60 kilometers (40 miles) north of Gwoza," Umar wrote.

Boko Haram has previously targeted both schools and students within the African country. In the local language, the extremist group's name stands for "Western education is sinful."

The Boko Haram leader in the video admitted that some of the victims may call themselves Muslims, but he considered them infidels under the group's strict interpretation of Shariah law. According to the Associated Press, he also made an exception to holding prisoners as described by the prophet Mohammed.

"We felt this is not the right time for us to keep prisoners," the leader said. "That is why we will continue to see that the grounds are crimsoned with the flowing blood of prisoners."

According to another Associated Press article, Boko Haram has made inroads within the African region it operates. The terrorist organization has launched strikes across the border in Cameroon, recruited people from Chad to enforce control in its areas, and displaced tens of thousands of Nigerian refugees.

"We are concerned about the increasing regionalization of Boko Haram," said Comfort Ero, Africa director for the International Crisis Group.

Ero told the Associated Press that cooperation between the neighboring countries in tackling Boko Haram is weak.

"None of the sides is willing to share information with the other," Ero said. "There's always been a lack of confidence in terms of shared regional security."

Ero added that the local population did not trust the capability of Nigeria's military to combat the terrorists. The Associated Press reported that a court-martial this week sentenced 54 Nigerian soldiers to death by firing squad for refusing to fight the extremists.

Despite the setbacks in the fight, Jean-Pierre Mbida, a soldier with the Rapid Intervention Battalion, told the Associated Press that the Nigerian army has been looking for hideouts in the area.

"We will continue monitoring the area in the hope of uncovering any other Boko Haram hideouts and training grounds," Mbida added.

The Associated Press also reported that Cameroon's army took out a Boko Haram training camp in the country's northern region on Sunday.