Reports say that the killings happened when a Cameroonian paramilitary unit was enforcing a $300 (£230) fishing levy.
Nigeria’s parliament is investigating reports that 97 fishermen have been killed in the Bakassi peninsula, which the country ceded to Cameroon.
Nigerian Interior Minister Abdulrahman Dambazau accused Cameroon of breaching an agreement to protect its citizens.
The Cameroonian government is yet to comment.
Cameroon took control of oil-rich Bakassi in 2008 after an International Court of Justice ruling, ending years of border skirmishes
Nigeria earlier this week summoned the Cameroonian ambassador to lodge a formal protest note