Video claims to show 15 girls taken by Boko Haram in 2014

A video purporting to show some of the more than 200 girls kidnapped by Nigerian-based Islamist militant group Boko Haram has surfaced on the abduction's second anniversary.

In the video, thought to have been made in December and obtained by CNN, 15 girls are expressionless as they state their names to a man heard off camera.

"We are all well," said one of the girls in the video, first broadcast Wednesday. She then encouraged the Nigerian government to meet Boko Haram's demands, which were not stated.

CNN reported that the video was made as "part of negotiations between the government and Boko Haram."

Although Nigerian officials have alluded vaguely to possible talks, there have been few clear details even as the militants continue to wage attacks. The kidnapping of the 276 schoolgirls gained worldwide attention, and Nigeria's president, Muhammadu Buhari, pledged to bring them home. Several girls managed to escape, but 219 are still missing.

The last time the girls were seen publicly was in a May 2014 video released by Boko Haram. In Nigeria, rumors have swirled over their possible fate. Some women held by Boko Haram in other areas have described a widespread campaign of sexual abuse and forced marriages by the extremists.

The newly released video shows the missing girls with flowing head scarves that conceal everything but their faces.

Despite the sketchy information provided in the video, Nigeria's information minister, Lai Mohammed, told CNN that the girls in the video appeared "under no stress whatsoever."

CNN also spoke to mothers and a classmate of the kidnapped girls, who said they recognized the young women in the video. "I felt like removing her from the screen," said Rifkatu Ayuba, whose daughter was among the 15 girls shown.

Although thousands of people have been kidnapped by Boko Haram in recent years, the girls, taken from the northeastern town of Chibok, became an international symbol of the conflict. The United States has dispatched surveillance drones and military trainers, and activists around the world united on social media behind the hashtag #BringBackOurGirls.

"Two years on, the Chibok girls have come to symbolize all the civilians whose lives have been devastated by Boko Haram," said Amnesty International's Nigeria director, M.K. Ibrahim.

The United Nations is helping to support some of the people who escaped from the Islamist group, many of whom live in sprawling displacement camps and abandoned buildings.

The girls are thought to be in the remote Sambisa forest in northeastern Nigeria. Although the country's military has dislodged militants from cities and towns, a search-and-rescue operation in the forest is thought to be far more difficult.

The video's broadcast coincided with a report by the U.N. children's agency UNICEF accusing Boko Haram of sharply increasing the use of child suicide bombers - with girls accounting for more than three-quarters of them - in Nigeria, Cameroon and Chad. Some of the girls are thought to have been kidnapped by the extremists.