Nigeria’s military claimed Thursday that Abu Musab al-Barnawi, the leader of an Islamic State-linked extremist group blamed for killing hundreds in the northeast, had died. There was no immediate confirmation from the militants.

At a news conference, Nigeria’s chief of defense staff, Gen. Lucky Irabor, told reporters: “I can authoritatively confirm to you that Abu Musab is dead.” He gave no further information, and it was not possible to independently corroborate the claim.

The announcement came only five months after al-Barnawi and his forces claimed responsibility for killing rival extremist leader Abubakar Shekau.

Some reports said al-Barnawi had been fatally wounded during clashes with yet another rival extremist faction, but the military gave no details about how it had confirmed his death.

Al-Barnawi was a teenager when his father, Mohammed Yusuf, was killed by Nigerian security forces in 2009.

The death of the founding Boko Haram leader has fueled a more than decade-long insurgency against the Nigerian government, ultimately expanding to neighboring Niger, Chad, and Cameroon.

Shekau took command of the group after Yusuf’s death but clashed frequently over the years with al-Barnawi, who reportedly at one point was picked instead by the Islamic State organization to lead Boko Haram. Instead, a breakaway faction was formed in 2016 that became known as the Islamic State in West Africa Province, or ISWAP.

Unlike Shekau’s group, which often violently targeted civilian populations, ISWAP under al-Barnawi targeted the Nigerian military and those who aided the soldiers. But it drew heightened global concern when it began targeting civilians working for international aid organizations in the northeast in a series of kidnappings and killings.

The faction still led by Shekau, meanwhile, weakened in recent years and his death was announced in May. ISWAP then sought to expand its reach, but al-Barnawi failed to win over thousands of Shekau’s followers and many surrendered to the Nigerian military instead.

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.