Abu Musab Al Barnawi, leader of the ISIS affiliate in West Africa, Iswap, is dead, Nigeria's top general said on Thursday.
Iswap is an offshoot of the Boko Haram insurgent group that has been fighting against the Nigerian armed forces for 12 years. The two militant groups later turned on each other.
The conflict between the insurgents and Nigeria's armed forces, which has also spread to neighbouring Chad and Cameroon, has left about 300,000 dead and millions dependent on aid.
"I can authoritatively confirm to you that Abu Musab is dead," Lucky Irabor, the chief of defence staff, told reporters at the presidential villa in Abuja, without elaborating.
Vincent Foucher of France's National Centre for Scientific Research, an expert on the insurgent groups, said sources told him Al Barnawi was wounded in August during a clash against Boko Haram fighters and died later, possibly in September.
He said that while it was hard to get solid information, the report of Al Barnawi's death seemed plausible as the Iswap leader had issued a number of lengthy audio recordings in May and June but had gone completely quiet since August.
If confirmed, Al Barnawi's death would be the third of an Islamist insurgent group leader in West Africa this year, after Boko Haram's Abubakar Shekau in May and Adnan Abu Walid Al Sahrawi, leader of the ISIS branch in the Sahel, in August.
Since Shekau's death, thousands of Boko Haram fighters have surrendered to the Nigerian armed forces, but Mr Foucher said Al Barnawi's death was unlikely to have a similar impact on Iswap as the group had already weathered leadership changes.
Al Barnawi had stepped aside between 2019 and 2021, with two or possibly three other leaders taking over during that period.
"The situation of the two groups is very different," he said. "Shekau was the autocratic leader of an organisation centred around him."
Boko Haram founder's son
Al Barnawi was the son of Boko Haram's founder, Muhammed Yusuf, whose killing by police in 2009 was one of the triggers for the group to launch a full-scale insurrection in north-east Nigeria.
After Yusuf's death, Shekau became the Boko Haram leader. Under his leadership, it carried out a campaign of bombings, killings and mass abductions. In 2014, the group gained worldwide notoriety when it abducted 270 girls from their school in the town of Chibok.
Shekau pledged allegiance to ISIS in 2015, but the following year the extremist group named Al Barnawi as its leader in West Africa.
Shekau rejected his demotion and the two split, with Al Barnawi moving his Iswap fighters to the shores of Lake Chad, where they became the dominant insurgency.
In June, Al Barnawi announced in an audio recording that Shekau had died in May after detonating an explosive device while being pursued by ISWAP fighters following a battle.
Nigerian authorities erroneously announced Shekau's death several times in previous years.
France announced a month ago that its forces had killed Al Sahrawi. His group operated in the Sahel, a strip of land below the Sahara Desert that includes countries such as Mali, Niger and Burkina Faso.
The level of co-ordination between the West African and Sahel-based affiliates of ISIS is not clear, but there have been increasing signs of contact between the two in recent years, particularly as the Sahel-based militants extend their influence in southern Niger.