He told the BBC that the militant group could no longer mount "conventional attacks" against security forces or population centres.
It had been reduced to fighting with improvised explosives devices (IED) and remained a force only in its heartland of Borno state, he said.
Boko Haram has been described as one of the world's deadliest terror groups.
Critics of the government argue that it has exaggerated the scale of its success against the militants, and that each time the army claims to have wiped out Boko Haram, the militants have quietly rebuilt.
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