Nigeria's air force said it had killed a number of senior Boko Haram fighters and possibly their overall leader, as U.S. Secretary of State John Kerry arrived for talks on tackling the militants.

Government planes attacked the Islamist group inside the Sambisa forest in its northeast heartland on Friday night, the air force said on Tuesday, saying it had only just confirmed details of the raid.

"Their leader, so called 'Abubakar Shekau', is believed to be fatally wounded on his shoulders," the statement by military spokesman Colonel Sani Kukasheka Usman added, without going into details on the source of its information.

The military has reported Shekau's death in the past, only to have a man purporting to be him appear later, apparently unharmed, making video statements. There was no immediate reaction from the group, which communicates with the media only by videos.

Nigeria has been pushing the United States to sell it aircraft to take on Boko Haram - a group that emerged in northeast Borno region seven years ago and has killed an estimated 15,000 people in its fight to set up an Islamist state.

Under Nigeria's last president, Goodluck Jonathan, the United States had blocked arms sales and ended training of Nigerian troops partly over human rights concerns such as treatment of captured insurgents.

But the new administration of President Muhammadu Buhari has argued its human rights record has improved significantly enough to lift the blockade.

There was no immedaite comment from Kerry's camp on the raids but he was due to speak in remote northwestern city of Sokoto later on Tuesday before travelling to Abuja to meet Buhari, officials said.

In May, U.S. officials told Reuters Washington wanted to sell up to 12 A-29 Super Tucano light attack aircraft to Nigeria in recognition of Buhari's reform of the country's army. Congress needs to approve the deal.

A Nigerian judicial inquiry said this month the army killed 349 people from the minority Shi'ite Muslim sect last December in a series of clashes for which troops involved should be prosecuted.

Two weeks ago Boko Haram published a video apparently showing recent footage of dozens of school girls from the northern city of Chibok kidnapped two years ago, saying some of them have been killed in air strikes.

The air force had denied it had killed any of the girls in air strikes. Authorities said in May that one of the missing girls had been found and Buhari vowed to rescue the others.