6 May 2014 Last updated at 20:24 BST US Secretary of State John Kerry has said the US is willing to provide intelligence and hostage negotiation expertise to assist Nigeria in the search for more than 230 kidnapped girls. The vast majority of the girls were seized from their school, in Borno, Nigeria, on 14 April, and the leader of the Islamist group Boko Haram has threatened to sell...