The Boko Haram group intends to sell hundreds of school girls who were abducted in Nigeria last month.
The girls were taken from a boarding school in Chibok, in the northern state of Borno, on the night of 14 April. About 230 are still missing.
In a video obtained by the AFP news agency on Monday, Boko Haram leader Abubakar Shekau said: "I abducted your girls".
In the video, Abubakar Shekau said the girls should not have been in school in the first place, but rather should get married.
"God instructed me to sell them, they are his properties and I will carry out his instructions," he said.
However, a BBC correspondent noted that the Boko Haram leader did not state the number of girls abducted, nor where they were taken or are now.
The girls were in their final year of school, most of them aged 16 to 18.
AFP said there are reports that some of them may have already been sold as brides across the border in Chad and Cameroon for $US12.
In a TV broadcast on Sunday, President Goodluck Jonathan said he did not know where the girls were but everything was being done to find them. It was his first comment on the abductions.
Boko Haram means "Western education is forbidden".
The United States has condemned the kidnapping as an outrage. The White House said President Barack Obama's national security team was considering how it could help in the search.