Nigeria's military has killed more than 65 members of criminal gangs known as bandits, linked to most of the country's mass kidnappings, a security report said on Sunday.

The offensive was carried out in the northwestern Zamfara state where police on Saturday confirmed a mass kidnapping carried out earlier in the week.

Police there confirmed there had been a "mass" abduction of villagers in raids by armed gangs on Thursday night, but gave no figures.

Residents, however, say that seven people may have been killed and 150 abducted when large numbers of heavily armed men invaded six villages in the Bukkuyum local government area.

Bandits killed in 'major breakthrough'

Police said a hunt has been launched for the attackers.

Sunday's security report said at "least 65 bandits" had been killed, in what it called a "major breakthrough."

But the "massive seven-hour ground and air offensive" was in Tsafe, a district around 200 kilometres from where the recent kidnappings occurred.

Zamfara is one of several states in northwest and central Nigeria facing insecurity posed by criminal gangs. Known locally as bandits, they carry out deadly raids on communities, kidnap residents for ransom, and burn homes after looting them.