| This file image of Boko Haram shows Abubakar Shekau |
Abu Musab al-Barnawi, named by ISIS last week as the new governor of its so-called West Africa Province, alleged that Shekau had killed fellow Muslims including his own fighters, neglected hungry women and children, and failed to provide food and weapons to fighters.
His audio message apparently was made on Friday and posted by the New York-based Sahara Reporters, a Nigerian newsgroup.
Shekau responded in a video posted on YouTube, saying al-Barnawi is not qualified to lead the group but insisting that "we have not reneged on our loyalty to the leadership of (Abu Bakr) al-Baghdadi," the ISIS leader.
The video, which was posted on Sunday night and removed by YouTube for violating its standards, ends with Shekau firing repeatedly in the air. He is flanked by two fighters hefting rocket-propelled grenade launchers.
The video starts with an unidentified masked man in front of a large group of armed fighters announcing their refusal to follow al-Barnawi and calling Shekau "our leader." Then Shekau, with his trademark bushy beard and camouflage, threatens more attacks and warns "President (Muhammadu) Buhari, very soon you will see us inside your home, the presidential palace."
The in-fighting could further weaken the Boko Haram militants, who are on the run from a multinational force in northeast Nigeria. The seven-year Boko Haram uprising has killed more than 20 000 people, forced 2.2 million from their homes and spread across Nigeria's borders.