Gen. Lucky Irabor, Nigeria’s chief of defense staff, told reporters: “I can authoritatively confirm to you that Abu Musab is dead.”

He gave no further details. It was not possible to independently corroborate the claim and the military gave no further information about how it knew he had been killed.

Al-Barnawi’s father, Mohammed Yusuf, had been the founding leader of Boko Haram, the Islamic extremist group that has been carrying out an insurgency for more than a decade now.

The violence has spread to neighboring Niger, Cameroon and Chad as well, destabilizing the Lake Chad region.

Al-Barnawi frequently clashed with the man who replaced his father, Abubakar Shekau, and broke away in 2016 to form the Islamic State in West Africa Province, or ISWAP.

Concern has mounted about ISWAP in recent years especially when the group began targeting civilians working for international aid organizations in the northeast. The faction led by Shekau had appeared weakened and in May it was announced that he had been killed during clashes with fighters linked to Al-Barnawi.

Security analysts say that Al-Barnawi, however, had failed to win over thousands of Boko Haram members who had been loyal to Shekau and many surrendered to the Nigerian military instead.

Unlike Boko Haram, which often violently targeted civilian populations, ISWAP under al-Barnawi targeted the Nigerian military and those who aided the soldiers.

“It has always been ISWAP’s policy to establish a decent relationship with Muslim civilians, taking taxes in exchange for protection and a degree of law and order,” said Vincent Foucher of the International Crisis Group.

The conflict in northeast Nigeria has directly caused the death of 36,000 people, according to U.N, officials, with more than 2.3 million people displaced.