Warren Stephens, the US’s ambassador to the UK, said while the “ideal” outcome would be for the UK not to transfer sovereignty of the Chagos Islands, it was the “best deal on the table for successive UK governments”.
Echoing the president, Stephens said the US “retains the right to maintain and to reinforce our security interests on Diego Garcia if needed in the future”.
Trump’s previous criticism of the deal came during an international row over his threats to take control of Greenland.
At the time, Sir Keir accused Trump of making the comments to pressure the UK over Greenland.
A draft law to ratify the Chagos Islands deal is making its way through Parliament but has been delayed since the president’s outburst.
Sir Keir has insisted the deal is necessary to protect the continued operation of the base, amid previous attempts from Mauritius to dispute the legality of British sovereignty over the islands.
A Downing Street readout of Thursday’s phone call between Sir Keir and Trump said the pair had “agreed on the importance of the deal to secure the joint UK–US base on Diego Garcia, which remains vital to shared security interests”.
The readout added: “The UK and US will continue to work closely on the implementation of the deal, they agreed.”
The deal has been heavily criticised by the Conservatives and Reform UK, who have called for the agreement to be scrapped.
Conservative shadow foreign secretary, Dame Priti Patel, said Trump’s statement “recognises a critical weakness in the surrender deal” about the lease arrangements.
“Keir Starmer and Peter Mandelson’s shameful Chagos surrender remains an absolutely terrible deal for Britain,” Dame Priti said.
“The Conservative Party’s view is unchanged,” she added. “We have led the fight against this appalling surrender and we will continue fighting it to the end.”