The World Court has backed Mauritius in a colonial-era dispute over the Chagos Islands, saying Britain's handling of decolonisation and the displacement of islanders from the Indian Ocean archipelago had been unlawful.
After gaining the islands in the early 1970s, Britain evicted almost 2000 residents to Mauritius and the Seychelles to make way for the US military base on the island of Diego Garcia.
In a non-binding advisory opinion, the top United Nations court for disputes between states said Britain's 1968 decolonisation of the islands had not been lawful and that Britain should relinquish control over the territory "as soon as possible".
Reading a summary of the 14-member tribunal's decision on Monday, presiding judge Abdulqawi Yusuf said Britain was "under obligation to bring to an end the administration of Chagos Islands as rapidly as possible".
The UN General Assembly asked the court in February 2017 to weigh in on whether the process has been concluded lawfully.
During court hearings, Mauritius said it had been forced to give up the remote archipelago to gain independence from Britain during the decolonisation process. Britain maintained that Mauritius had given up the islands willingly.
The court found the agreement between Britain and Mauritius at the time had not been "based on the free and genuine expression of the will of the people concerned" and thus did not comply with standards for self-determination.