A new video believed to be from Nigerian terror group Boko Haram shows more than 100 kidnapped Christian schoolgirls praying to Allah, and the Islamic terror group’s leader – who was reportedly negotiating with the government – saying he will hold the girls until imprisoned militants are freed.

Boko Haram leader Abubakar Shekau is seen on the 27-minute video, obtained by the Associated Press, announcing the girls have converted to Islam.

"Praise be to Allah, the lord of the world," chant the girls in the video, as they are seen wearing black and gray hijabs and reciting the Koran in Arabic as they make Islamic declarations of faith. Many of the girls -- who range in age from 15 to 18 -- are barefoot in the video. Some appear fearful, others desolate, and one said in the video that they had not been harmed, the BBC reported.

Three of the girls are shown speaking in the video. Two say they were Christian and have converted to Islam, while the other says she is Muslim.

"These girls, these girls you occupy yourselves with... we have indeed liberated them. These girls have become Muslims," Shekau says in the video.

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The majority of the abducted girls are believed to be Christians, although there are also some Muslims among them.

Shekau also says he would release the girls in exchange for prisoners. There is no indication of when or where the video was recorded, but the location appears to be rural.

When asked about the option of trading the girls for imprisoned militants, U.S. State Department spokesperson Jen Psaki said Monday, that is up to Nigeria. “As you know, Nigeria is in the lead. We are simply supporting their efforts. As you know also the United States' policy is to deny kidnappers the benefits of their criminal acts including ransoms or concessions,” Psaki said at a press briefing.

The video received Monday by the AP came through channels that have provided previous messages from Boko Haram leader Shekau, who speaks in the video in the Hausa language of northern Nigeria. He is shown in military fatigues cradling an assault rifle on the video, which is imprinted with the Boko Haram insignia of a Koran resting on two crossed assault rifles and below the black Jihadi flag.

The United States put a $7 million bounty on Shekau's head last year.

The video is the first sighting of the abducted girls since more than 300 were taken April 14 from their school in the northern town of Chibok by Islamist militants. Although more than 50 girls escaped their captors and are now safe, at least 276 remain missing.

The search so far has centered on the Sambisa forest, with Nigerian troops being aided by advisers from the U.S., Britain and France.

Pentagon spokesman Col. Steve Warren clarified the U.S. presence in Nigeria for reporters Monday, saying there are more than 50 U.S. military personnel and advisors based at the Nigerian Embassy to help “advise and assist” in the search for the missing girls. The teams have expertise in “communications, logistics, civil affairs, and intelligence,” Warren said.

"There are no plans to put additional U.S. military forces on the ground in Nigeria," Warren added.

When asked about the video, Psaki said U.S. intelligence agents are hoping to use it to help rescue the girls.

“We have no reason to question its authenticity. Our intelligence experts are combing through every detail of the video for clues that might help in ongoing efforts to secure the release of the girls,” Psaki said.

The video emerged Monday as the Nigerian government reportedly made "indirect contact" with the terrorist group. The report from Sky News did not specify how the two sides got in touch, but a special adviser to Nigerian President Goodluck Jonathan told Sky News that Nigeria would not pay to secure the girls' release, "because the sale of human beings is a crime against humanity."

The Nigerian government has been heavily criticized for how it has conducted its search for the missing girls, who were taken after taking final exams. On Friday, the group Amnesty International claimed that Nigerian security forces were aware that a convoy of fighters from Boko Haram was approaching the town of Chibok four hours before the kidnapping, but did nothing to stop the kidnappings.

It is believed that 53 girls were able to escape the kidnappers. One of them, 19-year-old Sarah Lawan, told the Associated Press that her ordeal was "too terrifying for words," and added that she was afraid to go back to school.

Boko Haram, whose name, loosely translated, means "Western education is forbidden," is believed to have killed approximately 1,500 people in Nigeria so far this year, and has been waging an insurgency in the country for the past five years.

Shekau claimed credit for the abductions in a video last week, saying, "I abducted your girls! By Allah, I will sell them in the marketplace!"

"This is a clear case of mismanagement of a small group of bandits who have been allowed to really grow into a monstrous terrorist organization that we now have," Atiku Abubakar, former vice president of Nigeria, told Sky News.

The search has been made more difficult by the lack of information regarding the girls' possible whereabouts, with speculation suggesting that they have been split into four groups, with some believed to have been taken across Nigeria's border.

Sky News reports that militants have likely laid booby traps and land mines to prevent searchers from finding the girls. In addition, two bridges crossing Nigeria's borders with Chad and Cameroon have reportedly been destroyed in the past week.

The Associated Press contributed to this report