The leader of the Nigerian militant group Boko Haram, Abubakar Shekau, has killed himself, rival Islamist militants said in an audio recording. In audio obtained by news agencies, the Islamic State West Africa Province (Iswap) said Shekau died detonating explosives on himself after a battle between the two groups. Shekau was reported dead last month and has been reported killed before. Neither Boko Haram nor the Nigerian government have confirmed his death. What did the recording say? In the undated audio recording, a voice thought to be that of Iswap leader Abu Musab al-Barnawi said Shekau "killed himself instantly by detonating an explosive". Iswap fighters hunted down the warlord and offered him the chance to repent and join them, al-Barnawi said. "Shekau preferred to be humiliated in the afterlife than getting humiliated on earth," he said. When reports of Shekau's death in a clash circulated last month, the Nigerian army said it would investigate. Army spokesman Brig Gen Mohammed Yerima told the BBC at the time the army was looking into what happened, but that it would not issue a statement until it got definitive proof. One journalist with close links to security agencies said that Shekau died when Iswap attacked Boko Haram positions in the Sambisa forest, north-east Nigeria. He has been reported dead numerous times before, only to resurface.