Assessing the threat of Boko Haram in Nigeria
14 May 2014 Last updated at 23:35 BST
Nigeria's president has said there is no question of swapping any of the girls kidnapped by the violent Islamist group, Boko Haram, for prisoners of the insurgency held by the government.
It is now a month since Boko Haram militants abducted more than 200 girls in the northern state of Borno.
Boko Haram, whose name means "Western education is forbidden" in the local Hausa language, is notorious for raiding towns and villages, burning homes, looting banks and police stations, and killing people.
John Simpson reports.