Nigeria’s parliament is investigating reports that 97 fishermen have been killed in the Bakassi peninsula, which the country ceded to Cameroon.
Reports say that the killings happened last week when a Cameroonian paramilitary unit was enforcing a $300 (£230) fishing levy.
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.
Survivors of the attack have been arriving back in Nigeria with injuries, reports the BBC’s Naziru Mikailu in the capital, Abuja.
Nigeria’s lower house of parliament resolved that it will investigate the reports in view of the 2005 Green Tea agreement between the two countries, to protect the citizens of the ceded areas from harm.
A five-year UN-backed transition period was put in place exempting the area’s residents, many of them Nigerian fishermen, from paying tax.
Nigeria earlier this week summoned the Cameroonian ambassador to lodge a formal protest note.
• Cameroon based its claim of sovereignty on maps dating back to the colonial era
• It was administered by Nigeria from independence in 1960 until 2008
• Nigeria and Cameroon nearly went to war over Bakassi in 1981 and bloody clashes claimed 34 lives in 1994
• In 2002, the International Court of Justice ruled in Cameroon’s favour
• 14 August 2006: Nigerian troops withdrew but the area remained under Nigerian administration
• 14 August 2008: Nigeria fully ceded the territory to Cameroon
• 15 August 2013: Cameroon took over full sovereignty and a tax-free exemption for residents came to an end