Nigeria's air force said it had killed a number of senior Boko Haram fighters and possibly their overall leader, and U.S. Secretary of State John Kerry pledged to consider ways to ramp up military assistance to Nigeria to defeat the militant group.
Government planes attacked the Islamist group inside the Sambisa forest in its northeast heartland on Friday, the air force said, adding that it had only just confirmed details of the impact 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 Obama administration has paid close attention to the fight against the militant group which has declared allegiance to Islamic State and destabilised a whole region by attacking Nigeria's neighbours.
Nigerian President Muhammadu Buhari did not address the reported air raid on the militants and Kerry did not raise it in their meeting in Abuja, a senior State Department official said. "It didn't come up," the official said in an interview, "I don't think (Buhari) has enough information and we didn't have enough information to raise it."
On his first stop in the remote northern city of Sokoto, the top U.S. diplomat said the struggle against Boko Haram would succeed only if it tackled the reasons why people join militant groups and gained the public's trust.
"It is understandable that, in the wake of terrorist activity, some are tempted to crack down on anyone and everyone who could theoretically pose some sort of threat. But extremism can’t be defeated through repression or fear," he said.
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. The militants have killed an estimated 15,000 people in their 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 argues its human rights record has improved significantly enough to lift the blockade.
The senior State Department official said there was now a recognition by the Nigerian military of the need to pay attention to human rights. "While they are not perfect, they are conscious" of the issue, the official added.
In May, U.S. officials told Reuters that 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.
Kerry said Buhari had made "a strong start at all levels of government" since taking office in May 2015, without referring specifically to rights abuses.
In the meeting with Buhari at the sprawling presidential villa, Kerry promised to look at ways to ramp up military cooperation with Nigeria to "bring this fight to a close," the State Department official said, adding that the militant group no longer held any territory in the north.
Kerry "made very, very strong commitments to the (Nigerian) government that we are going to look at what we can do differently," the official said, adding that the package for the aircraft was still being considered and needed congressional approval.
"We are working with (Nigeria) to make sure they can afford it, and they know how to use" the aircraft, the official added.
There was no immediate reaction from Boko Haram, which communicates with the media only by videos. The military has reported the death of Boko Haram's Shekau in the past, only to have a man purporting to be him appear later, apparently unharmed, making video statements.
There have been recent signs of rifts between at least parts of Boko Haram and Islamic State. The global militant organisation announced a new leader for what it described as its West African operations this month - an account that Abubakar Shekau appeared to contradict in a later video message.