Tonga's Surveyor General, Tevita Malolo, has dismissed claims from Fiji of ownership of the Minerva reef.
The reef, which is south of both Fiji and Tonga, has been claimed by the people of Ono-i-Lau in Fiji's Lau Group as the traditional fishing ground of their ancestors for centuries.
The islanders now say they may have overlooked Minerva Reef when registering their fishing and land rights and have asked the government to secure it for them, despite it being officially claimed by Tonga.
But Mr Malolo says the reef, which the kingdom considers two islands, was proclaimed as Tonga's by its king in 1972.
He says claims by Fiji of ownership are baseless.
"That's rubbish. We enforced national jurisdiction twelve miles around the two islands there. No formal objection was given to our government."
Tevita Malolo says Tonga has never entered into any formal agreements allowing Fiji to fish in the waters around the reef.
