The Tonga government says there's strong evidence that the Fiji military vandalised a navigation beacon on the Minerva Reefs earlier this year.
Tonga and Fiji have been at loggerheads over the ownership of the Reefs for years.
In a statement, Tonga's chief secretary, Busby Kautoke, says the matter has become woven into what he calls the humanitarian rescue earlier this month of a former Fiji military officer.
Lieutenant Colonel Ratu Tevita Uluilakeba Mara has since found sanctuary in Nuku'alofa, evading bail in Fiji in a sedition case.
Mr Kautoke says much has been made of the question of sovereignty in an incident which is wholly concerned with a rescue at sea and a purely humanitarian act.
He says disputes in international law are never simple, but require diligence and clarity.
He added that the overall question of sovereignty should therefore address the violation of Tongan sovereignty on the Minerva Reefs, early this year.