Lt. Col. Musa Sagir, the spokesman of the military, quoted intelligence report as saying that Boko Haram chief Shekau may have died between July 25 and August 3.
"Shekau was mortally wounded in the encounter and was sneaked into Amitchide - a border community in Cameroon for treatment," Sagir said, adding that a recent video on Shekau was not real but dramatised by one of his followers to hoodwink the sect members and the public.
Angered by the terrorist activities of Shekau and his sect, the US had placed a bounty of USD 7 million on his head.
More than 2,000 people have beeen killed since 2009 when Shekau inherited the leadership of the sect from its founder, Muhammed Yusuf who was killed in police custody.
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In May, President Goodluck Jonathan declared a state of emergency in three out of the 36 states in a bid to stop the insurgency.
Boko Haram has vowed to introduced an Islamic system in most or if possible all parts of Nigeria by force.