(VoA) – Nigeria’s President Muhammadu Buhari has invited the United Nations to help negotiations to exchange the kidnapped schoolgirls from Chibok for detained leaders of Boko Haram, a government statement said Thursday. Buhari’s government has been criticized for failing to free the Chibok girls by parents of the abducted students, community leaders and human rights activists. Boko Haram has kidnapped thousands of people, but the mass abduction of 276 schoolgirls in April 2014 brought international condemnation of Nigeria’s home-grown Islamic extremist group. Dozens of the girls escaped, but 217 remain missing.