An audio recording purportedly from Abu Musab al-Barnawi, the leader of the Islamic State West Africa Province, or ISWAP, said Shekau detonated explosives killing himself after a battle between the two groups.
The audio message follows media reports last month that Shekau, one of Africa’s most wanted men, blew himself up to evade capture by ISWAP fighters.
Neither Nigerian authorities nor Boko Haram have confirmed Shekau's death.
There had been several false reports about Shekau’s death in the past, with Shekau later appearing in videos to refute them.
Al-Barnawi, a son to the founding leader of Boko Haram, the late Mohammed Yusuf, made the statement in an audio message heard this week by The Associated Press in the native Kanuri language.
The audio message, which last about 28 minutes, had what is reportedly al-Barnawi's voice, lacing his speech with quotes from the verses of the Quran. The audio was obtained from a former jihadist who provides intelligence to the government and is familiar with al-Barnawi’s voice.
“He never thought this would happen to him even in his dream, but by the power of God we destabilized him; he became confused and fled to forest where he spent five days, wandering and stranded,” he said. “We followed him again where we faced him with heavy fire. He ran away, then our troops called on him to surrender so that he would be punished.”
Shekau was asked to surrender in order to be pardoned or reinstalled as a leader.
“We kept assuring him that we were not out to kill him, but he refused. To him it’s better to die than to surrender,” he said.
He went out to describe Shekau as “a defiant and corrupt leader” whose fighters were celebrating instead of mourning his death.
“This was someone who committed unimaginable terrorism. How many has he wasted? How many has he killed? How many has he terrorized?” he said.
ISWAP broke off from Boko Haram in 2016 following a dispute between Shekau and al-Barnawi. Both jihadi groups have also been fighting each other over territory since they fell out.
The Nigeria-based Boko Haram has been waging a bitter war against Nigeria, Cameroon, Niger and Chad since 2009.
Boko Haram under Shekau’s leadership has carried out numerous suicide bombings targeting markets, crowded bus stations, churches, mosques and media houses. A Boko Haram bombing in 2011 at the U.N. building in Nigeria's capital, Abuja, killed 21 people and wounded 60 others.
Boko Haram attacks on towns and villages mainly in northeast Nigeria have left tens of thousands of people dead and displaced more than 2.3 million others.
In February 2014, Boko Haram killed 59 male students in an attack at the Federal Government College Buni Yadi. Two months later, the group shocked the world when it abducted 276 teenage schoolgirls from the Government Girls Secondary School, Chibok, Borno State. Shekau appeared in a video saying that the girls would be forced into marriage because girls as young as 9 are suitable for marriage. While many of the girls have either escaped or been released, 112 of them are still missing.
The Boko Haram leader was notorious for using underage boys as child soldiers, while underage girls and young women have been used as suicide bombers in recent years.
Some gruesome Boko Haram videos have shown captives, including security personnel, aid workers and others, executed — sometimes by beheading.
Shekau had bounties on his head, with a reward of up to $7 million offered by the United States in 2012.
If indeed Shekau, the driving force behind Boko Haram, has died, that will likely weaken Boko Haram and make it possible for ISWAP to take over vast territories under Boko Haram control in Nigeria’s northeastern states of Yobe, Borno and Adamawa.
A stronger ISWAP will be bad news for the Nigerian military, as the group appears to constitute a greater threat against the Nigerian army, carrying out attacks on highly fortified military bases.
Many attribute ISWAP’s recent successes to new tactics of buying over the local population with food and money.
Sam Olukoya reported from Lagos.