The UK government has defended a deal to give the Chagos Islands to Mauritius and lease back a key military base, following criticism from US President Donald Trump over its handling.

In a post on social media, Trump labelled the move as an “act of great stupidity” and “total weakness”, months after he and senior US officials endorsed it.

In response, the UK government said it would “never compromise on our national security”, while the prime minister’s official spokesperson insisted the US still supported the move.

The UK signed the £3.4bn ($4.6bn) agreement in May, under which it would retain control of a UK-US military base on the largest of the islands, Diego Garcia.

In a post on his Truth Social platform on Tuesday morning, Trump said: “Shockingly, our ‘brilliant’ NATO Ally, the United Kingdom, is currently planning to give away the Island of Diego Garcia, the site of a vital U.S. Military Base, to Mauritius, and to do so FOR NO REASON WHATSOEVER.

“There is no doubt that China and Russia have noticed this act of total weakness.”

He added: “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.”

Responding, the prime minister’s official spokesman said that the US supports the deal and “the president explicitly recognised its strength last year”.

He added that it was also backed by the UK’s Five Eyes allies, the other members of which – besides the UK and US – are Canada, Australia, and New Zealand.

Asked if he could categorically say the Chagos deal would go ahead, even though it is still going through Parliament, the spokesman said: “Yes. Categorically, our position hasn’t changed.”

Earlier, a UK government spokesperson said it had 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”.

They added that the agreement had secured the operations of the joint US-UK military base “for generations, with robust provisions for keeping its unique capabilities intact and our adversaries out”, and noted the deal had been welcomed by allies including the US.

UK Foreign Office minister Stephen Doughty later said the government “will of course have discussions with the [Trump] administration in the coming days to remind them of the strength of this deal and how it secures the base”.

Mauritius’ attorney general Gavin Glover has said he still expects the agreement to go ahead.

In a statement he said it was “important to remember” that the deal was “negotiated, concluded and signed exclusively between the United Kingdom and the Republic of Mauritius”.

He added: “The sovereignty of the Republic of Mauritius over the Chagos Archipelago is already unambiguously recognised by international law and should no longer be subject to debate.”

The agreement followed a long-running dispute between the UK and Mauritius – a former British colony – about sovereignty over the Chagos Islands.

The Chagos Islands were separated from Mauritius in 1965, when Mauritius was still a British colony. Britain purchased the islands for £3m, but Mauritius has argued that it was illegally forced to give them away as part of a deal to gain independence.

Under the deal agreed in May last year, the UK would hand over sovereignty of the islands to Mauritius, while retaining control of the military base on Diego Garcia.

It would lease back Diego Garcia for a period of 99 years – at an average cost of £101m a year. Prime Minister Sir Keir Starmer said that was necessary to protect the base from “malign influence”.

Before signing the deal, the UK offered Trump an effective veto, because of its implications for US security.

Allies of the president had criticised the plan, but during a meeting with Sir Keir in the Oval Office last February, Trump said “I think we’ll be inclined to go along with your country”.

After the agreement was signed in May, US Secretary of State Marco Rubio said in a statement that Washington “welcomed” the deal.

He said it secured the “long-term, stable, and effective operation of the joint US-UK military facility at Diego Garcia”, which he described as a “critical asset for regional and global security.”

Rubio added that “President Trump expressed his support for this monumental achievement during his meeting with Prime Minister Starmer at the White House.”

A government bill to implement the agreement between the UK and Mauritian governments is currently in its final stages.

On Tuesday, Conservative leader Kemi Badenoch said in a post on X that the prime minister now had “the chance to change course on Chagos”.

She said that “paying to surrender the Chagos Islands is not just an act of stupidity, but of complete self sabotage”.

Reform UK leader Nigel Farage, who has long been a critic of the deal, said in a post on X: “Thank goodness Trump has vetoed the surrender of the Chagos islands”.

Liberal Democrats leader Sir Ed Davey said Trump’s comments showed Sir Keir’s approach to the US president “has failed”.

“The Chagos Deal was sold as proof the government could work with him, now it’s falling apart,” Davey said in a post on X.

“It’s time for the government to stand up to Trump; appeasing a bully never works.”

Labour MP and chair of the Foreign Affairs Committee, Emily Thornberry, told BBC Radio 4’s Today programme that while the UK should take Trump “seriously”, it should not take his comments “literally”.

She described his comments on Tuesday as an example of “presidential trolling”, saying she was “in favour of keeping calm and trying to sit this out”.

Two British Chagossian women born on Diego Garcia – Bernadette Dugasse and Bertrice Pompe – want the right to return to their place of birth and say they were excluded from discussions over the deal.

Pompe told the BBC she views the US president’s criticism of the deal as a “good thing” but “only words”.

Over WhatsApp, Dugasse said: “I want the deal to stop and not [see] money [given] to the Mauritius government.”

She said Chagossians should be allowed to “sit at the table and decide our future”.

Additional reporting by Alice Cuddy