In a diplomatic blow to Britain, the United Nations voted on Thursday to ask the International Court of Justice to rule on the fate of the British-ruled Chagos islands, which host an important military base.
The Indian Ocean archipelago has been at the center of a decades-long dispute over Britain's decision to separate it from Mauritius in 1965 and set up a joint military base with the US on Diego Garcia, the largest of the islands.
The measure was approved by a vote of 94-15 with 65 abstentions, notably from many European countries including Germany and France.
The vote was seen as a test of Britain's ability to rally support at the United Nations from fellow Europeans after it voted to leave the European Union.
Britain and the United States had strongly appealed to the 193-nation assembly to vote against the measure, arguing that it was a bilateral dispute.
British Ambassador Matthew Rycroft argued that the General Assembly should not intervene in a bilateral dispute that London was seeking to address through negotiations.
"How many other bilateral disputes left over from history could be brought before the General Assembly in this way?" asked Rycroft.
"The present draft resolution could set a precedent that many of you in this hall could come to regret."
Russia and China abstained, refusing to back Britain at the General Assembly. Most EU countries also opted for an abstention, except for Albania, Bulgaria, Croatia, Hungary, Lithuania and Montenegro.
The ICJ's opinion would be non-binding, but it would lend support to a campaign by Mauritius for the return of the Chagos Islands.
Mauritian Defence Minister Anerood Jugnauth told the UN assembly that bilateral talks with Britain had failed and that his country's sovereignty over the islands would not threaten the status of the Diego Garcia base.
Diego Garcia was used by the US Central Intelligence Agency as an interrogation center for terror suspects from Afghanistan after the September 11, 2001 attacks.
"More than five decades have passed, and now is the time to act," said the defense minister.
Mauritius argues that it was illegal for Britain to break up its territory while the Indian Ocean country was under British colonial rule. Mauritius won independence in 1968.
Britain rejects Mauritius's sovereignty claim over the Chagos Islands, but has said it will return the archipelago to Mauritius when the military base is no longer needed, without specifying a possible date.
India and African countries voted in favor of the resolution.