A video purporting to show around 130 of the schoolgirls kidnapped in Nigeria almost a month ago, has been released by the Islamist group, Boko Haram.

The group's leader, Abubakar Shekau, said they would be held until all imprisoned militants had been freed.

Boko Haram abducted more than 200 girls in northern Nigeria on 14 April and threatened to sell them.

Nick Childs reports.