Boko Haram's leader Abubakar Shekau killed himself in a fight against rival jihadist fighters from the Islamic State West Africa Province (ISWAP), the group said in a recording released on Sunday.

ISWAP sent audio to Reuters and AFP news agencies in which their leader described how Shekau reportedly died.

A person purporting to be ISWAP leader Abu Musab al-Barnawi said that Shekau killed himself on May 18 after detonating an explosive device that he was wearing. "Shekau preferred to be humiliated in the afterlife than getting humiliated on Earth," he can be heard saying. "God has judged him by sending him to heaven."

ISWAP described in the audio how it sent out fighters to Boko Haram's enclave in the Sambisa forest, who found Shekau sitting inside his house and engaged him in a firefight.

"From there he retreated and escaped, ran and roamed the bushes for five days. However, the fighters kept searching and hunting for him before they were able to locate him," the voice said.

DW has been unable to independently verify the claims made by ISWAP in the audio message; the militant group offered no evidence to support them.

Boko Haram have not commented on Shekau's reported death, while the Nigerian army said it was investigating.

Shekau turned Boko Haram into a powerful insurgent group

He helped turn the militant group from a marginal Islamist outfit to one capable of carrying out a full-fledged insurgency in less than a decade, engaging in brutal murders, kidnapping and looting across the northeast of Nigeria.

As many as 30,000 people are estimated to have died from its terror activities, while it has forced around 2 million people to flee their homes, according to the UN refugee agency.

ISWAP were previously part of Boko Haram before splitting five years ago, pledging allegiance to the "Islamic State." 

The schism was caused by religious ideological disagreements over the use of female suicide bombers and the killing of Muslim civilians by Boko Haram, to which ISWAP reportedly objected.

jf/sri (AP, AFP)