The United Kingdom has announced that it is giving up sovereignty of the Chagos Islands to Mauritius in a deal that will secure the future of a key United States military base on the atoll of Diego Garcia while allowing islanders displaced for the past five decades a right of return.

The deal, announced jointly by the UK and Mauritius yesterday, grants the latter full sovereignty over the remote archipelago, guaranteeing the operation of the United States base for the next ninety-nine years.

The United Kingdom, which has controlled the region since 1814, detached the Chagos Islands in 1965 from Mauritius, a former colony that became independent three years later to create the British Indian Ocean Territory.