The Nigerian president, Muhammadu Buhari, has said the Boko Haram leader Abubakar Shekau is wounded in his first comments on military claims that the jihadi leader was injured in an attack.

Nigeria’s armed forces said on Tuesday that Shekau had been wounded in an airstrike on Boko Haram’s forest stronghold, but released no further statement or evidence confirming his condition.

“We learned that in an airstrike by the Nigeria air force he was wounded,” Buhari said in a statement from Nairobi, where he is attending a development conference.

“Indeed their top hierarchy and lower cadre have a problem,” Buhari said. “They are not holding any territory and they have split into small groups attacking soft targets.”

Buhari said Shekau had been “edged out” of the group, adding credence to claims that Isis-appointed Abu Musab al-Barnawi is now in charge of the insurgency.

Signs of a power struggle in the top echelons of the jihadi group appeared earlier this month when Shekau released a video denying he had been ousted.

Barnawi is believed to be the 22-year-old son of the Boko Haram founder Mohammed Yusuf, and was announced as the group’s leader by Isis this month.

Buhari made his remarks from Nairobi this weekend where he is attending the Tokyo International Conference on African Development, a summit designed to boost ties between Africa and Japan.

The president also said he was “prepared to talk to bona fide leaders of Boko Haram” to negotiate the release of 218 Chibok girls captured by the militants in 2014.

Boko Haram has ravaged north-east Nigeria in its quest to create a fundamentalist Islamic state, killing more than 20,000 people and displacing 2.6 million from their homes.

Turning to another major security concern in Nigeria, Buhari gave a warning to militants sabotaging oil infrastructure in the southern swamplands of the Niger delta.