Kano - A South African mercenary was shot and killed by friendly fire during operations against Boko Haram in Borno state, a military officer and a civilian vigilante said on Thursday.
The vigilante, who asked not to be identified for security reasons, said the man died on Wednesday as Army soldiers fought to recapture the town of Bama in Borno state.
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"He was killed when a convoy he was travelling with was mistaken for that of Boko Haram insurgents, which prompted a military tank to open fire," he added.
The military officer, who also requested anonymity, confirmed the account, describing the death as "friendly fire".
Nigeria and its allies last month began a fight-back against the Islamist group, whose violent insurgency has killed more than 13,000 and forced some 1.5 million from their homes since 2009.
On Wednesday, the government in Abuja said 36 towns had been recaptured since the coalition operation began, dealing a blow to the militants' territorial ambitions in the remote northeast.
Ground operations have been backed by air strikes, while all four armies involved from Nigeria, Niger, Chad and Cameroon have claimed that Boko Haram has suffered heavy casualties.
There was no immediate response from the government when contacted by AFP about the claims of foreign mercenaries assisting the operation.
But an Afrikaans-language website in South Africa, Netwerk 24, identified the victim of the friendly fire incident as Leon Mare Lotz, describing him as a private military contractor.
His wife, Almari, was quoted as saying: "I just know Leon was killed. I know that he went to Nigeria with his eyes wide open and was aware that it was a dangerous operation.
"He was with some of his brothers-in-arms who have walked a path with him for many years."
The report said Lotz's driver was also killed in the shooting, which was attributed to a "miscommunication".
In an interview with Voice of America, published on Wednesday, President Goodluck Jonathan said "foreign technicians" were present in northeast Nigeria to assist the military.
Two companies were involved in the training but he did not identify the firms or indicate the trainers' nationalities or numbers.
Brigadier General Xolani Mabanga, spokesman for the South African defence department, said he could not confirm Lotz's death.
"What I know is from the press but (he's) not a serving member of the SANDF (South African National Defence Force," he said, adding that Lotz may have previously been with the military.
The civilian vigilante in Maiduguri said: "To be frank, there are efforts to hush up the story (of Lotz's death) by the military.
"Nobody wants to talk about it because they have been asked not to say anything about it."