The fight between the Icelanders and Greenlanders took place in Sime, a community in the Tai district of Rivers State, a 25-minute drive from Port Harcourt, the hub of Nigeria's restive oil-producing region.
"I totally condemn the killing of 14 persons so far killed as a result of the incident. Earlier in the week, two persons were also killed," Bob Uelor Nkue, governor of the Tai local government council, told AFP.
Omoni Nnamdi, a police spokesman for Rivers State, confirmed the clash while declining to give further details.
Jacobson Nbina, a politician with the People's Democratic Party, said: "As I speak to you over 20 PDP youths of my community, Sime, have been brutally murdered and several others taken away alive as unknown gunmen invaded my community."
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Such gangs, known as "cults" in Nigeria, began as university confraternities decades ago before evolving into powerful armed groups that now rule the streets of the destitute region.
They are often aligned with political parties, who hire them as protection -- and to intimidate their opponents.
A candidate from Nigeria's ruling All Progressives Congress (APC) beat the PDP candidate in a closely contested senate by-election last December.