Sir Keir Starmer's Chagos Islands deal threatens America's nuclear deterrent capability in the region, Washington has warned ahead of Donald Trump's state visit.

The unprecedented intervention, reported by Facts4EU and shared exclusively with GB News, comes after the Prime Minister agreed to give Mauritius sovereignty over the British Indian Ocean Territory back in October.

The deal, which critics branded a "surrender", has implications for America due to the presence of a joint UK-US military base on Diego Garcia.

The base on Diego Garcia is located in a strategically crucial location in the Indian Ocean, with the airbase representing one of only two US strategic bomber bases in the Indo-Pacific region.

In addition to the B-1, B-2 and B-52 bombers operating from the island, the US also maintains a satellite control network and a naval support facility on Diego Garcia.

At the time of transfer, Foreign Secretary David Lammy insisted that the agreement "secures this vital military base for the future," he said.

The agreement the UK signed commits that the US will maintain access to Diego Garcia for the duration of the 99-year lease, with certain important measures to protect the base’s integrity, such as a 24-mile exclusion zone and a ban on foreign military presence on outer islands.

Despite Labour's assurances, Washington hawks long raised concerns that the deal leaves the vital US-UK military asset exposed to China, which wields influence over the Mauritian government.

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As a Facts4EU report explains, concerns over the proposed deal by the Labour Government and Mauritian policy on nuclear weapons have come to the fore after President Trump raised it during his recent trip to Scotland and is also being presented to Vice President JD Vance ahead of his visit to the UK in the autumn.

Now, in a major development in Washington on Tuesday, the Republican-led US House of Representatives Committee on Appropriations has formally raised concerns over the deal, highlighting its strategic implications for US national security and countering the rising threat from China.

Included in the recently released National Security, Department of State, and Related Programs Appropriations Bill for 2026, the Committee’s language makes clear that Diego Garcia remains a central pillar of Anglo-American power projection in the Indo-Pacific, and that the Chagos Islands deal now poses a serious risk to that posture.

It states: "United Kingdom and Chagos Archipelago —The Committee notes that with the growing challenge from the PRC the military facilities on the island of Diego Garcia are central to Anglo-American power projection and relative control of the Indian Ocean.

"Recognising the invaluable strategic importance and geographic relevance of Diego Garcia to the United States, the Committee encourages the Secretary of State to engage with His Majesty’s Government of the United Kingdom to ensure our long-term access to the facilities and that they remain integral to allied security.”

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This unprecedented intervention stems in part from Starmer Government’s agreement handing over sovereignty to a state bound by the Pelindaba Treaty, which prohibits nuclear weapons from being stationed or transiting its territory.

That treaty restriction includes Diego Garcia, once sovereignty formally transfers, meaning the UK and US could be legally blocked from deploying or supporting nuclear-capable assets from the base, even under the so-called "99-year lease".

However, another treaty could also block the US from deploying nuclear-capable assets in the region.

GB News | The Prime Minister has handed back the British-owned Chagos Islands to Mauritius after 200 years

Support for a nuclear-capable military facility is a key function of Diego Garcia.

The remote base regularly hosts US nuclear-powered cruise missile submarines (SSGNs) and submarine tender ships.

Elements of America’s airborne leg of its nuclear triad also frequent the Indian Ocean atoll – including B-2 nuclear-capable heavy bombers.

Under agreements between the UK and US for access to Diego Garcia, transferring nuclear-tipped missiles to and from the island is considered normal.

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The extent to which nuclear weapons are stored and stockpiled on Diego Garcia is unclear.

As the Facts4EU report explains, neither the UK nor the US administrations will confirm or deny that Diego Garcia, part of the Chagos Peninsula, is the site of a nuclear arsenal.

That said, retired military personnel have confirmed unofficially and 'on deep background' that this is the case.

Even without any such confirmation, logic dictates that the base, given its vital geo-strategic importance, has always been used in this way.

However, it is clear that Diego Garcia’s strategic value to the US would be much diminished if nuclear material were prohibited in the Chagos Archipelago.

This capability now hangs in the balance due to a little-known treaty in the UK called the "African Nuclear-Weapon-Free Zone".

As Facts4EU explains, the UK has specific derogations in respect of the British Indian Ocean Territory, which includes the Chagos Islands, but the government of Mauritius is a firm advocate.

With UK sovereignty of the Archipelago ceded by Starmer to Mauritius, it seems inevitable that the demands of this Treaty will be exercised, regardless of what it might say in terms of 'protections' contained in the Treaty signed with Mauritius by Lammy.

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The Treaty negotiated by David Lammy with close involvement from the Prime Minister still has to be ratified by Parliament

Reacting to the latest development, US commentator and head of the Thatcher Institute of the US Heritage Foundation, Dr Nile Gardiner, said: "The fight continues in the United States against the disastrous Chagos Islands surrender by the Starmer Labour Government, a huge gift to Communist China.

"In a major development in Washington, the Republican-led House of Representatives Committee on Appropriations has raised the issue of the hugely controversial, high-risk Chagos Islands deal between the UK and Mauritius (a close ally of Beijing), the growing threat from Communist China, and the implications for the future of the vital US military base at Diego Garcia.

"The Congressional Committee urges the US Secretary of State to engage further with the British Government on assurances that vital US strategic interests are protected. The fight continues in the United States against the disastrous Chagos Islands surrender by the Starmer Labour Government, a huge gift to Communist China.

"We can expect significantly increased scrutiny of the Starmer Government's Chagos Islands deal on Capitol Hill, especially ahead of the upcoming State Visit to the UK in September by President Trump.

"The Chagos issue is not over in Washington, and major red flags are being raised in the United States."

The Treaty negotiated by David Lammy with close involvement from the Prime Minister still has to be ratified by Parliament.

At present, it is not clear the extent to which a full Parliamentary debate will be allowed, with a proper amount of time devoted to it.

There is a cross-party motion signed by 83 MPs from the Conservatives, Reform UK and some Northern Ireland MPs and other moves which we are not able to publish at this stage.

"Overall, the way this whole affair has been handled is yet one more example of how the Government is behaving increasingly like a dictatorship and is riding roughshod over normal democratic and legal oversights," adds Facts4EU.