The Nigerian militant group Boko Haram has released a video said to show some of the scores of girls who were abducted from a boarding school last month.
In the images, delivered to news organizations and posted on YouTube on Monday, about 100 girls are shown covered in gray and black veils and reciting in Arabic. It is not clear where or when the video was recorded.
An estimated 276 schoolgirls have been missing since April 14, when gunmen stormed their school in Chibok, in Nigeria's northeastern Borno state, and drove off with them in trucks. At least 53 girls have managed to escape, according to police.
Boko Haram's leader, Abubakar Shekau, appears in the video wearing military fatigues and holding an assault rifle. He says the girls have converted to Islam and won't be released until imprisoned militants are freed.
Nigerian Interior Minister Patrick Abba Morro rejected the offer of a prisoner exchange, telling the BBC that it is "absurd" for a "terrorist group" to try to set conditions.
The mass kidnapping and the government's failure to rescue the girls have provoked outrage in Nigeria, a country of 170 million divided between the predominantly Muslim north and the mainly Christian south. Last week, Nigeria accepted offers of help from the United States, Britain and other countries.
Boko Haram, which bitterly opposes secular education and Western culture, has carried out dozens of school attacks since 2012, killing scores of students and teachers. It has closed nearly all of the schools in Nigeria's vast northeastern desert region and wants to establish Islamic law throughout Nigeria.