US President Donald Trump lambasted Britain’s deal to cede sovereignty of the Chagos Archipelago including an island with an important US-UK air base as an act of “total weakness” and “great stupidity” underlining why he wants to acquire Greenland.

Washington had last year given its blessing to the deal which gave the Indian Ocean islands to Mauritius but retained UK control of the Diego Garcia base under a 99-year lease.

But Trump reversed that with a typically blunt Truth Social post saying: "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."

He added: "There is no doubt that China and Russia have noticed this act of total weakness ... 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."

Trump's attack heaps new strain on relations with Prime Minister Keir Starmer, who this week spoke out against his ambition to take over Greenland by any means to counter the encroaching presence of rivals China and Russia.

Responding to Trump's Chagos comments, the British government said the deal was made precisely for national security reasons. "We acted because the base on Diego Garcia was under threat after court decisions undermined our position and would have prevented it operating as intended in future," a spokesperson said.

The Chagos' six main atolls, among more than 600 islands, lie 500 km (300 miles) south of the Maldives and halfway between Africa and Indonesia, with about 4,000 people stationed there.

Britain forcibly displaced up to 2,000 indigenous Chagossians in the late 1960s and 1970s to establish the base on the Diego Garcia atoll, but has given sovereignty to former colony Mauritius which it is paying 101 million pounds ($136 million) per year to secure the installation.

Base used for strikes from Yemen to Afghanistan

Recent operations launched from Diego Garcia include bombing strikes against Houthi targets in Yemen in 2024 and 2025, humanitarian aid deployments to Gaza and attacks against Taliban and al Qaeda targets in Afghanistan in 2001.

British senior minister Darren Jones said the Chagos deal was already done and he could not see how it might be changed.

Britain had in fact delayed signing the deal until after Trump's inauguration in January 2025 to give his administration time to examine the plan. "President Trump expressed his support for this monumental achievement," US Secretary of State Marco Rubio said of the agreement in May last year.

Starmer had built a solid relationship with Trump, becoming the first leader to secure a deal to lower some tariffs, but that has been shaken with disagreement over Greenland and now the Chagos islands furore.

The British leader on Monday called for calm dialogue to avert a trade war over Greenland after Trump threatened new levies, urging the U.S. president to respect alliances.

Britain would be focusing on diplomatic channels to try to navigate Trump's aims, Jones said. "The prime minister has shown that private, proper British diplomacy can work," he told BBC Radio.

Britain's opposition Conservative Party leader Kemi Badenoch weighed in to agree with Trump on the Chagos islands, saying the "terrible" deal weakened UK security.

"Paying to surrender the Chagos Islands is not just an act of stupidity, but of complete self sabotage," she posted, adding that "unfortunately on this issue President Trump is right."

Some Chagossians, many of whom ended up living in Britain after being removed from the archipelago, have also opposed the deal on the grounds that they were not consulted.