A group of fighters from Nigerian Islamist group Boko Haram pledged allegiance to rivals the Islamic State West African Province (Iswap) weeks after the former group's leader died, according to a video seen by Reuters.

The video fuels fear that Iswap is consolidating control of the insurgency in northeastern Nigeria following the death of Boko Haram leader Abubakar Shekau last month. But not all observers are convinced the video is proof that all Boko Haram fighters are ready to join Iswap...