Sovereignty of the Falkland Islands rests with the UK, Downing Street has said, following a report the US could review its position on Britain's claim to the territory.

An internal Pentagon email reported by Reuters suggested the US was considering options to punish NATO allies it believed had failed to support its war on Iran.

The options discussed also included seeking Spain's suspension from NATO over its opposition to the war. BBC News has not been able to review the email.

A Pentagon spokesperson did not comment on the email's existence, but said it would ensure that the president has credible options to ensure that our allies are no longer a paper tiger and instead do their part.

As President [Donald] Trump has said, despite everything that the United States has done for our NATO allies, they were not there for us, the spokesperson added.

The Falkland Islands, a British overseas territory in the south-west Atlantic Ocean, remain the subject of a sovereignty dispute between Britain and Argentina.

Asked about the report, a No 10 spokesman on Friday said: The Falkland Islands have previously voted overwhelmingly in favour of remaining a UK overseas territory, and we've always stood behind the islanders' right to self-determination and the fact that sovereignty rests with the UK.

The prime minister's official spokesman also said the government could not be clearer about the UK's position, and that sovereignty rests with the UK and the islanders' right to self-determination is paramount.

He continued: We've expressed this position previously clearly and consistently to successive US administrations and nothing is going to change that.

Former Labour security minister Lord West described the Pentagon leak on the Falklands as quite extraordinary and a sign of a lack of understanding.

Lord West, who was an officer commanding HMS Ardent during the Falklands War, went on to characterize US Defence Secretary Pete Hegseth as thick and accused him of having a total lack of understanding about NATO.

Hegseth talks about the fact that NATO's never done anything for America, America's done so much for NATO, but the only time that Article 5 was invoked was by NATO, and it was to defend the United States, he said.

Under NATO's Article 5, an armed attack against one or more members is deemed an attack against all. The only time Article 5 has been invoked was after the 9/11 attacks on the US in 2001.

Previous US administrations have formally recognised the UK's de facto administration of the islands, but have not taken a formal position regarding sovereignty.

The Falkland Islands has complete confidence in the commitment made by the UK government to uphold and defend our right of self-determination, the islands' government said in a statement.

Conservative leader Kemi Badenoch said the reported US stance on the Falkland Islands was absolute nonsense, adding: We need to make sure that we back the Falklands. They are British territory.

Meanwhile, an official from NATO responded to the suggestion in the report that the US could push for Spain's expulsion from the military alliance, stating that its founding treaty does not foresee any provision for suspension of NATO membership, or expulsion.

Earlier, Spain's Prime Minister Pedro Sanchez stated: We do not work based on emails. We work with official documents and official positions taken, in this case, by the government of the United States.

As diplomatic tensions rise, this matter becomes increasingly critical, especially with King Charles III's upcoming visit to the US.