Kidnapped schoolgirls are seen at an unknown location in this still image taken from an undated video released by Nigerian Islamist rebel group Boko Haram. [Photo/Agencies]

LAGOS, Nigeria - Looking sad and frightened, dozens of barefoot girls sat huddled together wearing gray Muslim veils as they chanted Quranic verses in Arabic. Some Christians among them said they had converted to Islam.

In the video released Monday, the Boko Haram terrorist network offered the first public glimpse of what it claimed were some of the nearly 300 girls kidnapped from a Nigerian school a month ago and issued an ominous threat. The girls will not be seen again, the group's leader said menacingly, until the government frees his imprisoned fighters.

"I swear to almighty Allah, you will not see them again until you release our brothers that you have captured," Abubakar Shekau warned.

11 more girls kidnapped in Nigeria

It is not known how many suspected Boko Haram members are detained by security forces. Hundreds were killed last month when Shekau's fighters stormed the military's main northeastern barracks in Maiduguri, the birthplace of Boko Haram and the headquarters of a year-old military state of emergency to put down the 5-year-old Islamic uprising.

As the girls chanted Islamic verses, some clasped their hands together in what appeared to be the Christian style of prayer before quickly turning their palms upward, as Muslim worshippers do.

The girls' families have said most of those seized April 15 from a school in the northeastern town of Chibok are Christians.

It was impossible to fully authenticate the video, though parents were trying to turn on a generator in Chibok, hoping to watch the video and identify their daughters, said a town leader, Pogu Bitrus.

"There's an atmosphere of hope - hope that these girls are alive, whether they have been forced to convert to Islam or not," he told The Associated Press by telephone.

"We want to be able to say. These are our girls."

The video showed about 100 girls, indicating they may have been broken up into smaller groups as some reports have indicated.

Fifty-three girls managed to escape and 276 remain missing, police say.