Nigeria's military said it has killed 17 insurgents in an attack on two training camps belonging to the Boko Haram Islamist group.
One soldier was also killed in the firefight that broke out after they moved in on the camps, backed by helicopter gunships, the military said.
Spokesman Lt Col Sagir Musa said the "fortified" camps were in a forest and a game reserve in Borno State.
Boko Haram is seeking to establish an Islamic state in Nigeria.
The group has been blamed for the deaths of some 1,400 people in central and northern Nigeria since 2010.
The military "conducted two special operations supported by Nigerian Airforce helicopter gunship[s] to dislodge Boko Haram training camps" in the Ruwa forest and the Sambisa Game Reserve, Lt Col Musa said in a statement.
"The camp was properly… fortified and had training facilities, an armoury, accommodation, a drug store, kitchen, vehicle holding area, latrine and water points," he said.
Boko Haram has not yet commented on the incident.
The group was formed in Maiduguri, capital of the north-eastern Borno State, in 2002.