Boko Haram leader Abubakar Shekau vowed to sell hundreds of schoolgirls kidnapped in Northern Nigeria three weeks ago, in a new video obtained Monday by CNN.

“I abducted your girls,” the video said. “I will sell them in the market, by Allah.” The video appears to confirm unsubstantiated reports that some of the 223 girls still missing may have been sold as brides across Nigeria’s border with Chad and Cameroon for as little as $12, according to BBCnews.

Shekau said the abduction has caused outrage “because we are holding people (as) slaves.”

In a related development, the Associated Press and BBCnews said that police acting on the orders of Nigeria’s first lady, Patience Jonathan, arrested protesters speaking out against the Nigerian government’s apparent disinterest in finding the girls.

A leader of a protest march for the missing schoolgirls said Nigeria’s first lady expressed doubts there was any kidnapping and accused the protesters of belonging to the network blamed for the abductions. Then she ordered two of them arrested, the AP reported.

Saratu Angus Ndirpaya of Chibok said state security service agents drove her and protest leader Naomi Mutah Nyadar to a police station Monday after an all-night meeting at the presidential villa in Abuja, the capital. She said Nyadar are in detention.

Police could not be reached for comment. Ndirpaya says Patience Jonathan accused them of fabricating the abductions to give Nigeria’s government and her husband a bad name.