The US president said the UK's decision to cede the Chagos Islands to Mauritius is among the reasons he wants to take control of Greenland.
US President Donald Trump on Tuesday criticised the UK's deal to hand sovereignty of the Chagos Islands to Mauritius, calling it an "act of great stupidity" and "total weakness."
Trump said that relinquishing the remote Indian Ocean archipelago — home to a key joint US-UK military base on Diego Garcia, the largest island — was "another in a very long line of national security reasons why Greenland has to be acquired."
"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 said in a post on his social media platform Truth Social.
"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 added.
The UK signed the £3.4bn (€3.9bn) agreement with Mauritius in May, under which London will retain control of the Diego Garcia military base under a long-term lease.
Washington welcomed the deal at the time, saying then that it "secures the long-term, stable and effective operation" of the facility at Diego Garcia.
The US has described the base — home to about 2,500 mostly American personnel — as "an all but indispensable platform" for security operations in the Middle East, South Asia and East Africa.
Speaking on Tuesday, UK Cabinet Minister Darren Jones said that the agreement would "secure that military base for the next 100 years."
"The treaty has already been signed," Jones told Times Radio, adding that it could not be changed.
One of the last remnants of the British Empire, the Chagos Islands have been under UK control since 1814. The UK split the islands away from Mauritius — a former British colony — in 1965, three years before Mauritius gained independence.
Tensions rise over Greenland
Trump's latest remarks come as he ramps up his calls for the US to take control of Greenland, a self-governing territory of NATO member Denmark.
Trump has insisted the US needs the Arctic Island for security reasons against possible threats from Beijing and Moscow.
The US president has linked his aggressive stance on Greenland to last year's decision not to award him the Nobel Peace Prize, telling Norway's prime minister in a text message over the weekend that he no longer felt "an obligation to think purely of peace."
That followed his announcement that the US would implement a wave of increasing tariffs from February on goods from eight EU nations that have rallied behind Denmark.
US Treasury Secretary Scott Bessent said on Tuesday that relations with Europe remain strong. He urged trading partners to "take a deep breath" and allow tensions driven by the Trump administration's new tariff threats over Greenland to "play out."
"I think our relations have never been closer," he said on the sidelines of the World Economic Forum annual meeting in Davos, Switzerland.
In a sign of how growing tensions, thousands of Greenlanders protested over the weekend against any effort to take over their island. Greenland Prime Minister Jens-Frederik Nielsen said on Monday that the tariff threats would not change their stance.