(CNN)The UK must return the Chagos Islands to Mauritius "as rapidly as possible," the United Nations' highest court ruled Monday, branding its occupation of the Indian Ocean archipelago illegal.
The islands, which are home to US military base Diego Garcia, were separated from the former British territory of Mauritius during decolonization in 1968. The international Court of Justice (ICJ) has ruled that act was illegal under international law.
For years, the US base has been vital to the military, serving as a landing spot for bombers that fly missions across Asia, including over the South China Sea. The UN ruling raises questions about its future.
The decision by the ICJ is merely advisory. The matter of who holds sovereignty over the Islands, located more than 2,000 miles off the east coast of Africa, will now be debated by the United Nations General Assembly -- which referred the case to the ICJ despite London's protests.
"The United Kingdom is under an obligation to bring an end to its administration of the Chagos Archipelago as rapidly as possible, thereby enabling Mauritius to complete the decolonization of its territory in a manner consistent with the right of peoples to self-determination," the ICJ said in its judgment.
Carl Schuster, a former director of operations at the US Pacific Command's Joint Intelligence Center, said the ruling could force Washington to negotiate with Mauritius over the future of the Die