Gunmen have killed 17 people including five policemen in separate attacks in northwest Nigeria's Katsina state in the latest wave of violence in the region, police and a local official said Thursday.

The criminals, who maintain camps in a vast forest straddling Zamfara, Katsina, Kaduna and Niger states, were declared terrorists by Nigeria's government in January.

Late on Wednesday, a group of around 300 bandits on motorcycles attacked a police post near Gatakawa village in Kankara district, killing five policemen, local police spokesman Gambo Isah said.