Nigeria's Boko Haram: What You Need To Know
Nigeria's militant Islamist group Boko Haram, is fighting to overthrow the government and create an Islamic state.
It promotes a version of Islam that makes it "haram", or forbidden, for Muslims to take part in any political or social activity associated with Western society.
Boko Haram says it was behind attacks on churches which left more than 40 people dead on Christmas Day 2011, and also carried out a suicide attack on the UN headquarters in Abuja four months earlier.
Mansur Liman from the BBC's Hausa service explains the key facts about Boko Haram.