Abuja – The leader of the Boko Haram group is believed to be fatally wounded in an air strike carried out by the Nigerian military in the country's northeast, according to media reports citing a senior official sources.The report said a number of fighters were targeted last week in the Sambisa forest near Gambaru in Borno state, near the border with Cameroon."Their leader, so called 'Abubakar Shekau', is believed to be fatally wounded on his shoulders," the statement released on Tuesday from army spokesperson Colonel Sani Kukasheka Usman added.Usman also said three Boko Haram commanders Abubakar Mubi, Malam Nuhu and Malam Hamman, were confirmed dead with several others wounded.Al Jazeera's, Ahmed Idris, reporting from Abuja, said the airstrike happened when fighters had gathered for "some sort of a ceremony"."The attack happened on Friday on Shekau's camp. We know that the Chibok girls are held at the Shekau camp to which the Nigeria army said that they are doing everything possible to rescue them," our correspondent said. The claim comes as US Secretary of State John Kerry visits the country for talks likely to focus on the fight against Boko Haram, which launched an uprising in 2009.Nigerian forces, with the support of regional troops, have recently recaptured swathes of territory lost to the fighters.The mysterious Shekau's fate has been the subject of speculation recently amid claims he had been replaced by Sheikh Abu Musab al-Barnawi, the group's former spokesperson.Barnawi's appointment was contained in a magazine issued by the ISIL to which Boko Haram pledged allegiance in March last year.But only a week later, the shadowy Shekau surfaced in a video posted on social media, ridiculing suggestions of his death and looking more composed and energetic than in previous appearances.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. Boko Haram, which seeks to impose a strict Islamic law in Nigeria's mainly-Muslim north, has killed some 20 000 people and forced at least 2.6 million others to flee their homes since 2009.