Gunmen suspected to be gang members shot dead five local residents at the weekend near Nigeria's oil city of Port Harcourt, the police said on Monday.
Rivers state police spokesman Ahmad Mohammed said assailants on motorbikes opened fire on Sunday in the Agbonchia Eleme area, near the country's largest oil refinery.
"Five persons lost their lives," Mohammed told AFP in a text message.
"Preliminary investigations revealed the incident is related to cult (gang) activities. Investigations continue," he added.
Eleven suspects, including an alleged "vicious and notorious cultist" wanted by police, were later arrested during a police raid on the gunmen's hideout, said Mohammed.
Items recovered from the scene of the shooting included a jeep, two motorcycles and 20 expended shells of 7.62 mm ammunition, he added.
Oil-rich Rivers state, of which Port Harcourt is the capital, is notorious for kidnapping, oil theft and criminal activities by gangs.