Kano - Boko Haram's leader Abubakar Shekau has been injured and one of his deputies killed in an air strike in northeast Nigeria, civilian and security sources told AFP on Wednesday.Two Nigerian Air Force jets bombarded fighters who had gathered for prayers in Balla village, some 40km from Damboa, on the edge of the Sambisa Forest, last Friday."Shekau was wounded in the bombings and is believed to be receiving treatment near the Nigerian border with Cameroon around Kolofata," said one source with contacts within Boko Haram."His deputy, Abba Mustapha, alias Malam Abba, was killed in the attack along with another key lieutenant, Abubakar Gashua, alias Abu Aisha," he added.Babakura Kolo, a member of the civilian militia in the Borno state capital, Maiduguri, gave a similar account, saying "Shekau was injured and a number of commanders were killed."Among them is his deputy called Malam Abba. They suffered heavy casualties because the bombings targeted a large gathering of his followers attending Friday prayers."There was no immediate comment from the Nigerian military when contacted by AFP. The authorities have previously claimed to have killed Shekau on at least three occasions.In an emailed statement on Tuesday night, the air force said it had bombed "a gathering of Boko Haram terrorists" last Friday "in a village 3.42 km northeast of Mangosum".The "air interdiction mission" in the remote region involved three jets."Battle damage assessment conducted after the strike showed that several leaders of the Boko Haram terrorist organisation and their followers were killed during the attacks," it added.ReprisalsA senior military officer in Maiduguri confirmed the air force bombed Boko Haram positions "in the Damboa area on Friday where they hit the targets with precision"."We got intel (intelligence) that the terrorists were gathering at the location and we acted on the report," he added, requesting anonymity as he was not authorised to speak about the operation.He said he was unable to comment on Shekau but the source with contacts in Boko Haram said Mustapha was preaching when the first jet bombed the mosque at about 13:00.Moments later a second jet targeted worshippers as they fled."Shekau was just leaving a house nearby for the mosque when the first jet struck. He was injured in the second strike," said the source, describing the casualties as "huge"."They spent the rest of Friday and the whole of Saturday burying the dead," he said, without specifying numbers.Shekau had been bed-ridden for days with malaria before the attack, he added.Local people in the Konduga area said Boko Haram fighters went on the rampage following the air strike."They came by the river hurling insults at us, accusing us of providing information about their locations and movements to the military," said fisherman Ibrahim Bawa."They said we were responsible for the attack on their mosque which killed many of their people. They were very angry," added another fisherman, Usman Sallau.The jihadists rounded up six fishermen and slit their throats. Others escaped by swimming across the river, he said.Boko Haram has killed over 20 000 people since it took up arms against the Nigerian government in 2009 to establish a hardline Islamist state.The insurgency has decimated northeast Borno state with the violence displacing 2.6 million from their homes and causing a hunger crisis.After years of suffering humiliating losses to Boko Haram, the Nigerian military has reclaimed swathes of territory back from the jihadists.Yet despite claims that Boko Haram is a spent force, the Islamists still launch attacks.