Boko Haram

Nigerian militant group Boko Haram has pledged allegiance to Islamic State (IS), according to an audio statement. The message, which has not been verified, was posted on Boko Haram's Twitter account and is believed to be by the group's leader, Abubakar Shekau. Boko Haram began a military campaign to impose Islamic rule in northern Nigeria in 2009. The conflict has since spread to neighbouring states. It would be the latest in a series of groups to swear allegiance to IS. In the past Boko Haram is thought to have had links with al-Qaeda. IS took control of large swathes of territory in eastern Syria and across northern and western Iraq last year. The group aims to establish a "caliphate", a state ruled by a single political and religious leader according to Islamic law, or Sharia. Its leader, Abu Bakr al-Baghdadi, is known to his followers as Caliph Ibrahim.