Nigeria's military said Tuesday it believes an airstrike has "fatally wounded" Boko Haram leader Abubakar Shekau, but there was no way to confirm yet another claim of the death of Nigeria's Islamic extremist leader.

A statement does not say how the military got the information but identifies other commanders as "confirmed dead" in an air raid on Friday.

The statement comes as Secretary of State John Kerry is to meet in Abuja, Nigeria's capital, with President Muhammadu Buhari, on a visit to discuss Islamic extremism and regional security. Kerry, speaking Tuesday morning in northern Sokoto city, made no reference to the army's report.

Shekau, according to a BBC profile, is known as a “fearless loner” with a photographic memory, a complex and often paradoxical man who is part intellectual, part terrorist. His nickname — Darul Tawheed — translates as a specialist in Tawheed, or the concept of monotheism in Islam.

“He hardly talks,” one journalist, Ahmed Salkida, told BBC. “He is fearless … He is one of those who believes that you can sacrifice anything for your belief.” Shekau does not speak English, but is fluent in his native Kanuri, Hausa and Arabic languages. He reportedly does not even communicate directly with the group’s soldiers.

Shekau, according to those who study the group, is known for being particularly brutal.

“I enjoy killing anyone that God commands me to kill — the way I enjoy killing chickens and rams,” he said in a clip released in 2012 after an attack in Kano, Nigeria, that killed more than 180 people.

Shekau was Boko Haram’s second in command until founder Mohammed Yusuf was killed in a 2009 crackdown. Shekau was initially thought to have also been killed during those attacks, but he later surfaced in a video claiming to be the terror group’s new director.

Nigerian security forces have at least three times in the past declared that they have killed or fatally wounded Shekau, only to have him resurface in video and audio recordings. The military has said in the past that Boko Haram was using look-alike fighters to impersonate the supposedly dead leader.

The strikes came in "the most unprecedented and spectacular air raid" carried out by the Nigerian Air Force while Shekau was praying on Friday, Islam's holy day, at Taye village in the extremists' Sambisa Forest holdout in northeast Nigeria, according to the statement signed by army spokesman Col. Sani Kukasheka Usman.

"Those Boko Haram terrorist commanders confirmed dead include Abubakar Mubi, Malam Nuhu and Malam Hamman, amongst others. While their leader, so-called `Abubakar Shekau', is believed to be fatally wounded on his shoulders. Several other terrorists were also wounded," he said.

Shekau started the uprising in 2009 that has killed 20,000 people, driven more than 2.2 million from their homes, and spread across Nigeria's borders. It has been marked by deadly attacks and suicide bombings at schools, mosques and marketplaces and mass abductions including nearly 300 schoolgirls taken from a remote school in northeastern Chibok town in April 2014. Dozens escaped but 218 remain missing.

A video showing dozens of the girls last Sunday said Shekau is willing to negotiate a prisoner swap for detained Boko Haram commanders. President Buhari is under increasing pressure to rescue or negotiate the girls' release, but his spokesman has said officials are wary since previous negotiations failed because officials were duped into talks with the wrong people.

Boko Haram appears to be fractured by a leadership struggle as the Islamic State group announced it had a new leader. Shekau has insisted he is still in charge. He had pledged the group's allegiance to the Islamic State group last year -- giving ISIS its first franchise in sub-Saharan Africa.

The Associated Press contributed to this report.