Nigeria's air force confirmed it had carried out bombardments in northwestern Zamfara State on Tuesday, but a spokesman said he could not yet provide details on the numbers killed.

Northwestern and central Nigerian states have for years been terrorised by gangs, known locally as bandits, who raid villages and kill and abduct residents for ransom in rural areas where state presence is weak.

The gangs, notorious for mass kidnappings from schools and colleges in recent years, maintain camps hidden in a vast forest straddling Zamfara, Katsina, Kaduna and Niger states.

"Fighter jets conducted air strikes on bandits, I'm sure more than 100 were killed and almost twice that number were badly injured," one of the military officers involved in the operation said.

Another military official also confirmed a similar number. Both spoke to AFP anonymously because they were not authorised to speak about the operation.

Two local residents who described the bodies after the strikes also gave similar numbers.

Fighters from seven of the most active gangs had converged in an area on the border between Zamfara, Kebbi and Niger states with the intent of attacking villages and a nearby military base, according to the officers.

"Timely intelligence report was received and surveillance was conducted which determined their location and movement before fighter jets were deployed," the first officer said.

When asked for details, Nigerian air force spokesman Commodore Edward Gabkwet confirmed the air strikes.

"But I can't confirm numbers to you," he said.

- Ties with jihadists -

The bandits riding motorcycles were intercepted by the fighter jets at Dan Mani village in Sangeko district on the fringes of Kuyan Bana forest where they were bombarded, the second military officer said.

"Dead bodies, which were badly burnt, littered the bushes. They were so many that the bandits abandoned many to make room for the evacuation of the injured," the officer said.

"We don't have an exact number of the casualties but the dead were more than 100," he said.

The air strike was the second most intensive aerial operation against bandits in Zamfara since 2015 when the military deployed to fight the gangs.

Usman Tukur, a resident of Kuyan Bana area where the air strike was carried out, told AFP that dozens of bodies were left around the area after the bombardment.

"They were bombarded by fighter jets and a huge number were killed. Those who survived were seen fleeing with their injured comrades through villages in the area," he said.

"From our estimation, those killed were more than 100."

Another resident Mustapha Sarki Kaya gave a similar account, saying locals had seen the bandits burying their dead.

Nigerian officials have struggled to end the violence in the northwest and several peace deals and amnesties with the bandit militias have failed to work.

Although the bandits are motivated by financial gain with no ideological leaning, authorities and security analysts are worried by the increasing ties with jihadists waging a 14-year armed insurgency in Nigeria.