abuja islamist militant group boko haram kill 381 civilians nigeria cameroon since begin april right group amnesty international say tuesday testament militant group deadly resurgence nigerian military repeatedly say boko haram defeat recent months carry string lethal suicide bomb high-profile attack towns oil exploration team number deaths since april double precede five months amnesty say boko haram kill 223 civilians nigeria since april force women girls act suicide bombers drive sharp rise deaths northeast nigeria northern cameroon say amnesty boko haram commit war crimes huge scale exemplify depravity force young girls carry explosives sole intention kill many people possibly say alioune tine amnesty director west central africa nigeria deadly attack july militants abduct oil exploration team staff state oil firm university travel military convoy boko haram kill 40 people kidnap three others amnesty say boko haram suicide bombers kill 81 people nigeria since start april say amnesty cameroon islamist insurgency kill least 158 people period also link rise suicide bomb deadly kill 16 people waza july right group say 2.5 million people displace become refugees lake chad region include nigeria cameroon niger chad 7.2 million people lack secure access food conflict boko haram accord unite nations insurgency leave 20,000 people dead since begin 2009. boko haram resurgence kill 381 civilians since april amnesty