The Nigerian military has detained over two dozen soldiers and members of the police force over sales of weapons from military stockpiles to armed groups, including Islamist insurgents, a spokesperson said.

Africa's most populous country and biggest energy producer, Nigeria is battling insecurity on many fronts, including a long-running insurgency in the northeast and armed kidnapping gangs in the northwest.

Captain Reuben Kovangiya, spokesperson for the military's anti-insurgency operation, said the arrests were part of a crackdown on racketeering involving ammunition.

Local media reported that 18 soldiers, 15 policemen and eight civilians were taken into custody.

"It is part of the counter-arms and ammunition racketeering operation conducted in every theatre of operations," Kovangiya told Reuters. "If any personnel engage in any act that is inimical to the system, they are arrested and tried."

Kovangiya did not elaborate on the types and numbers of weapons sold but said the suspects would be prosecuted.

Nigeria has this year experienced a surge in attacks by militants from Boko Haram and its offshoot, Islamic State West Africa Province, who have overrun some military bases in the northeastern state of Borno.

In the course of most of the raids, militants have seized weapons from army bases.