The leader of Boko Haram vowed to sell hundreds of schoolgirls that were kidnapped in the north of the country two weeks ago, Agence France Press reports on Monday.

Abubakar Shekau, the infamous head of the Nigerian Islamist militant group, made the comments in a taped video message in which he also claimed responsibility for the mass abduction.

"I abducted your girls. I will sell them in the market, by Allah," Shekau said, according to AFP.

Armed militants abducted more than 300 Nigerian girls from their secondary school in Borno state on April 14, driving them off into the remote Sambisa forest. While some managed to escape, police said last week that 276 were still missing.

Civic organizations had warned earlier that the young women were being forced to marry extremists for as little as $12 and had been trafficked across the borders with neighboring Chad and Cameroon.

Also on Monday, Nigeria arrested the leader of a protest group that called on authorities to do more to find the kidnapped girls. A source told Reuters that Naomi Mutah Nyadar had been detained for allegedly falsely claiming that one of the abducted girls was her daughter.