The US president has called Britain's deal to lease back the Chagos Islands to Mauritius an act of "total weakness"

US President Donald Trump has criticized the UK's decision to hand over control of Diego Garcia in the Chagos Islands to Mauritius, calling it a "great stupidity" and a threat to US national security.

The Chagos Archipelago, comprising more than 60 islands, was separated from Mauritius by Britain in 1965, three years before the East African country gained independence. In 1966, the largest island - Diego Garcia - was leased to the US for military use, and around 2,000 inhabitants were displaced. Mauritius has since sought to reclaim the territory.

Last May, UK Prime Minister Keir Starmer signed an agreement transferring sovereignty of the domain to Mauritius. However, the deal allows Washington and London to retain control of the joint military base on Diego Garcia for an initial period of 99 years at a reported total value of $3.9 billion. The decision came six years after the International Court of Justice advised that the UK should end its administration of the area "as rapidly as possible."

In a post on Truth Social on Tuesday, Trump expressed "shock" at Britain for giving away the "extremely important land" and "site of a vital US Military Base," warning that "there is no doubt that China and Russia have noticed this act of total weakness."

"These are International Powers who only recognize STRENGTH, which is why the United States of America, under my leadership, is now, after only one year, respected like never before," he said.

Trump highlighted his administration's focus on protecting US military interests, urging Denmark and its European allies to "DO THE RIGHT THING" regarding Greenland, which he has insisted on acquiring.

Last year, when Britain signed the deal transferring sovereignty of the Chagos Archipelago in the Indian Ocean to Mauritius, Starmer claimed that Trump, who had returned to office around four months earlier, supported the move.

In response to Trump's remarks, Darren Jones, the chief secretary to the prime minister, confirmed in an interview with Sky News that the deal was "welcomed at the time by the American administration and also by European allies."

Russian Foreign Minister Sergey Lavrov also weighed in on the dispute at a press conference on Tuesday, condemning major powers, including the UK, for still holding several territories - including the Chagos Islands - in violation of UN resolutions.