LONDON - A 2025 deal between the UK and Mauritius to hand over the Chagos Islands "secures the operations of the joint US-UK base" there, British media quoted a British government spokesperson as saying on Tuesday.

This came after US President Donald Trump accused the act of "great stupidity" earlier on Tuesday.

"Shockingly, our 'brilliant' NATO Ally, the United Kingdom, is currently planning to give away the Island of Diego Garcia, the site of a vital US Military Base, to Mauritius, and to do so FOR NO REASON WHATSOEVER," Trump posted on social media.

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"The UK giving away extremely important land is an act of GREAT STUPIDITY, and is another in a very long line of National Security reasons why Greenland has to be acquired," he added.

The British government spokesperson said the UK "will never compromise" on national security, and Britain acted because a joint US-UK base on Diego Garcia, the largest island of the Chagos islands, was "under threat after court decisions undermined our position and would have prevented it operating as intended in future."

In 2019, the International Court of Justice, the principal judicial organ of the UN, said that Britain had illegally split the islands and should give up control of them.

READ MORE: Mauritius to regain sovereignty over Chagos Archipelago from Britain

British Prime Minister Keir Starmer last year signed an agreement transferring sovereignty over the Chagos Islands to Mauritius. The deal cedes British control of the Chagos islands to the Mauritian government. Under the terms of the agreement, Mauritius will lease the Diego Garcia military base back to Britain and the United States.

The islands were separated from Mauritius in 1965, when Mauritius was still a British colony. Britain then invited the US to build a military base there, which saw thousands removed from homes.