Washington: The Islamic State (IS) terrorist group has announced that its leader and self-proclaimed caliph of the Muslim world, Abu Bakr al-Baghdadi, has accepted the pledge of allegiance from the Nigeria-based Boko Haram.

A 28-minute audio message purportedly from an IS spokesman posted online, said that the caliphate, or the Islamic State, has expanded to western Africa and congratulated "our jihadi brothers" there, according to a CNN report on Thursday.