Mauritius has launched a legal action against the UK to contest its creation of a Marine Protection Area around its Chagos Islands in the Indian Ocean.
The case comes after a US cable released by Wikileaks revealed UK and US officials discussing the park.
A UK official is quoted as saying it should put an end to any possibility of the displaced islanders returning.
Some 2,000 residents were forced out when the British colony was leased to the US in the 1960s for an air base.
Many of the former residents now live in Mauritius.
They have been campaigning for the right to return for many years and have a case pending at the European Court of Human Rights.
The marine reserve's creation was announced in April 2010 by then UK Foreign Secretary David Miliband.
A US cable from May 2009 quotes a discussion about the park with Foreign Office official Colin Roberts.
"He asserted that establishing a marine park would, in effect, put paid to resettlement claims of the archipelago's former residents," the cable said.
The Mauritian Prime Minister Navinchandra Ramgoolam said his government had filed a case before the International Tribunal for the Law of the Sea in Hamburg.
"By creating the protected marine area, Great Britain did not take into account Mauritius' rights and those of the Chagossians it shamefully evicted from Chagos," AFP news agency quotes Mr Ramgoolam as saying.
The archipelago in the Indian Ocean is one of the world's richest marine ecosystems.
Mauritius has for years claimed sovereignty over the islands, which lie about 1,000km (about 600 miles) to its north-east.