Four policemen were among 15 persons killed during attacks in Rivers, Cross River and Kano states on Tuesday night.
Suspected cultists reportedly gunned down six occupants, including two policemen, in a Toyota car in Port Harcourt, Rivers State, while two policemen were shot dead at Kwana Hudu, Nasarawa Local Government, Kano State
This came hours after gunmen killed two policemen and injured one in Kano.
The Port Harcourt killings, which took place at about 11pm, created panic in the area as residents fled for fear of reprisals.
Victims were trailed by their assailants from a drinking joint.
An eyewitness, Mr. James Ibe, said about five gunmen trailed the car up to Harbour Road and opened fire on its occupants.
He stated that the hoodlums did not take any thing from their victims, adding that the bullet-riddled car was abandoned by the gunmen.
Police Public Relations Officer in the state, Mr. Ben Ugwuegbulam, confirmed the incident.
An eyewitness told the News Agency of Nigeria in Kano that gunmen attacked a police roadblock in Kwana Hudu in the evening, killing their victims.
Police Public Relations Officer in the state, Magaji Majiya, said the police were on the trail of the gunmen.
Meanwhile, a communal clash between Adadama and Igbo Amabana in Abi Local Government, Cross River State claimed no fewer seven lives.
Both neighbouring communities, located in the Central Senatorial District of the state, have been engaged in a running battle over land.
The bodies of three men were seen at Adadama, along the Ugep-Abomege road, which leads to Ebonyi State.
Police Public Relations Officer in the state, Mr. John Umoh, confirmed the development, saying policemen had been deployed in the area.