LONDON -- British Prime Minister Keir Starmer on Thursday signed an agreement transferring sovereignty over the Chagos Islands to Mauritius.

The deal formally cedes British control of the Chagos Archipelago to the Mauritian government. Under the terms of the agreement, Mauritius will lease the Diego Garcia military base -- located within the archipelago -- back to Britain and the United States.

Starmer said the full rationale behind the decision remains "highly classified." He noted that failure to reach a settlement could have led Mauritius to pursue legal action at international courts, where Britain was likely to lose, potentially facing additional penalties.

The signing proceeded after a temporary injunction issued by the British High Court early Thursday was lifted later in the day.

US Secretary of State Marco Rubio welcomed the agreement in a social media post, describing it as "a historic deal."