British Prime Minister Keir Starmer has blocked a request from US President Donald Trump to allow US forces to use UK air bases during any preemptive attack on Iran, saying it could break international law, according to multiple reports in British media citing government sources.

According to The Times of London, which first reported the split over airbase access, Starmer has denied the use of RAF Fairford in England and Diego Garcia – the British overseas territory in the Indian Ocean – for any strike on Iran.

The two bases have long served as crucial overseas US military staging posts for operations far from home, with Diego Garcia a key airfield for the US’ heavy bomber fleet.

The Times reports Britain is concerned that allowing the US to use the bases “would be a breach of international law, which makes no distinction between a state carrying out the attack and those in support if the latter have ‘knowledge of the circumstances of the internationally wrongful act.’”

The Times cited UK government sources. The BBC, The Guardian and The Telegraph also subsequently published their own reports on the UK blocking access to the bases, citing sources.

American requests to use UK bases for operational purposes historically have been considered on a case-by-case basis, with precise criteria withheld for security reasons under long-standing agreements.

“All decisions on whether to approve foreign nations’ use of military bases in the UK for operational purposes considers the legal basis and policy rationale for any proposed activity,” Veterans Minister Al Carns wrote in response to questions from independent British member of parliament Jeremy Corbyn, according to a January report from the UK Defence Journal.

Starmer and Trump held a phone call on Tuesday evening, with readouts saying the two discussed peace in the Middle East and Europe.

The following day Trump took to his Truth Social platform to withdraw support for a deal that would see sovereignty over the Chagos Islands, the Indian Ocean chain that is home to the joint US-UK Naval Support Facility Diego Garcia, handed to Mauritius in return for a 99-year lease on the military base.

CNN has approached the White House for comment.

Britain had split the Chagos Islands from Mauritius before that colony gained independence, something that has been a source of diplomatic friction as well as multiple legal battles with locals who were evicted. In 2019, the International Court of Justice ruled Britain should return the islands “as rapidly as possible,” so that they could be decolonized.

A deal to return them has been making its way through British government channels since, with London arguing a lease compromise would ward off further expensive and likely futile legal battles while maintaining military access in the Indian Ocean.

After initially opposing the UK-Mauritius deal, Trump in early February said it was the “best” Britain could get under the circumstances.

But as the US has been surging forces into the region for a possible attack on Iran, Trump reversed course, saying in a Truth Social post that Starmer is “making a big mistake” in agreeing to the lease deal with Mauritius.

“Prime Minister Starmer is losing control of this important Island by claims of entities never known of before. In our opinion, they are fictitious in nature,” Trump’s post said.

But just a day earlier, the US State Department issued a statement saying in part that Washington “supports the decision of the United Kingdom to proceed with its agreement with Mauritius.”

Asked about the discrepancy between the Truth Social post and the State Department statement, White House press secretary Karoline Leavitt said the president’s post should be taken as the “policy” of the Trump administration.

In his social media post, Trump directly referenced the two UK airbases, cited by British media, as important in a possible strike on Iran.

“It may be necessary for the United States to use Diego Garcia, and the Airfield located in Fairford, in order to eradicate a potential attack by a highly unstable and dangerous Regime,” Trump wrote.

Neither Diego Garcia nor Fairford, the key forward operating base for US strategic bombers in Europe, was used in last June’s one-time B-2 bomber strike on Iranian nuclear sites. In that case, the stealth bombers flew a round trip of about 37 hours from their home base in Missouri.

But analysts are expecting that any new US attack on Iran might be a much longer campaign, possibly of weeks or more.

In such a campaign, having the B-2s, as well as B-1 and B-52 bombers, using bases thousands of miles closer to Iran would enable quicker turnarounds to rearm and refuel for more strikes.

While the US may have access to other bases in friendly countries closer to Iran, using them could put its prized heavy bomber fleet in reach of retaliatory Iranian missile strikes.