The UK’s position on the Falklands is resolute and unchanging, Downing Street has insisted, after a leaked Pentagon internal email proposed the US should reassess its support for Britain’s claim to the islands because of a lack of support over Iran.

Keir Starmer’s spokesperson did not push back against the likely veracity of the email but insisted that the UK’s defence and security relationship with the US remained extremely strong.

The memo, reported on by Reuters, argues that the US could review a policy of endorsing European claims to longstanding “imperial possessions”, and highlighted sovereignty over the Falklands, the subject of the 1982 war between Britain and Argentina.

It was drawn up in response to White House frustration that other members of Nato did not provide sufficient support for the US-led 38-day bombing campaign against Iran.

It also argued that Spain should be suspended from Nato for refusing to allow US warplanes to be based in or fly over the country during Operation Epic Fury, though it is not clear if there are mechanisms for doing so.

When asked to comment on the email, Kingsley Wilson, the Pentagon press secretary, said: “As President Trump has said, despite everything that the United States has done for our Nato allies, they were not there for us.

“The war department [Department of Defense] will ensure that the president has credible options to ensure that our allies are no longer a paper tiger and instead do their part. We have no further comment on any internal deliberations to that effect.”

Asked about the email, Starmer’s spokesperson said: “We could not be clearer about the UK’s position on the Falkland Islands. It’s longstanding. It’s unchanged. Sovereignty rests with the UK, and the islands’ right to self-determination is paramount. That’s been our consistent position and will remain the case.”

The Falkland Islanders, he added, had “voted overwhelmingly and in favour of remaining a UK overseas territory, and we’ve always stood behind the islanders’ right to self-determination”.

Asked if the UK government was worried about a possible change of heart on the issue from Donald Trump’s administration, the spokesperson said not, adding: “We have got one of the most important security and defence relationships, if not the closest, that the world has ever seen, and it continues.”

Asked if the UK could defend the Falklands alone, the spokesperson said he could not answer “hypothetical” questions.

Though the Falklands proposal looks vague and there is no immediate sign of it being adopted, the reference to the islands appears deliberately designed to provoke a reaction in the UK, where memories of the 1982 war linger.

The US provided discreet support for the UK during the conflict, which followed Argentina’s invasion of the remote south Atlantic islands, including satellite and signals intelligence and Stinger hand-held missiles.

Britain recaptured the Falklands in June 1982 at the end of a bitter 74-day conflict, in which 255 members of the British armed forces, 649 Argentinians and three Falkland Islanders were killed.

Though there has been no return to hostilities, the status of the islands remains disputed by Argentina, now led by Trump’s ally President Javier Milei.

Starmer largely kept the UK out of the Iran war, but unlike other European countries did allow the US to fly B-1 and B-52 bombers on what were deemed defensive missions, including against Iranian missile launchers and anything used to target shipping in the strait of Hormuz.

Trump, however, repeatedly complained about the lack of military support provided by the UK, complaining that Britain only wanted to help in protecting the strait after the war was over, that the Royal Navy’s aircraft carriers were “toys”, and compared Starmer to Neville Chamberlain.

Asked if Starmer believed he was being pressured by Trump to change his stance, the spokesperson said: “The PM has said very clearly that he won’t be pressured on the Iran war. He will always act in the national interests of the UK and will not be dragged into this war.”

The public outbursts are markedly different from 1982, when the US president, Ronald Reagan, made clear his support for the British prime minister, Margaret Thatcher, in private. “We will do what we can to assist you. Sincerely, Ron,” he wrote shortly after the initial Argentinian invasion.

Spain’s prime minister, Pedro Sánchez, played down the reports. Speaking in Cyprus on Friday morning, where he was attending a meeting of EU leaders to discuss topics including Nato’s mutual assistance clause, Sánchez stressed that Spain was a “loyal” Nato member and one that complied with its responsibilities.

“We don’t work on the basis of emails; we work with official documents and statements made by the US government,” he added. “The Spanish government’s position is clear: absolute cooperation with allies, but always within the framework of international law.”

Sánchez – who has been the most vociferous European critic of the US and Israel’s war in Iran – angered Trump by refusing the US permission to use jointly operated bases in southern Spain. Trump responded by threatening to cut off all trade with Spain.

But Sánchez also went on to renew his criticisms of the US war. “The crisis that this illegal war has brought to the Middle East shows the failure of brute force – and has prompted demands for international law to be respected and for the multilateral order to be safeguarded and reinforced,” he said.