Nigerian troops killed 24 suspected Islamist insurgents in two attacks in the northeast and recovered some weapons, the army said on Tuesday.

Boko Haram and its offshoot Islamic State West Africa Province (ISWAP) have been fighting the Nigerian armed forces for more than a decade in a conflict that has killed hundreds of thousands and displaced millions.

Major General Christopher Musa, commander of the anti-insurgency task force, told Reuters that soldiers killed 16 Boko Haram insurgents a few kilometres from Maiduguri city, the capital of Borno state.

Musa said that during the encounter with the insurgents two gun trucks were seized and one was destroyed.

President Muhammadu Buhari has said security forces are making gains against insurgents in the northeast and also against armed bandits who have carried out kidnappings for ransom and killed hundreds in the northwest.

Last week, Nigeria's top general said ISWAP leader Abu Musab al-Barnawi was dead, without giving details.

Army spokesman Brigadier General Onyema Nwachukwu said late on Monday troops from a joint Nigerian and Cameroonian operation also killed four ISWAP members who attacked a forward army base in Borno.

The conflict between the insurgents and Nigeria's armed forces has also spread to neighbouring Chad and Cameroon.

Another four suspected insurgents died when their truck mounted with anti-aircraft guns drove over an improvised explosive device, Nwachukwu said.