The US has launched a review of its multi-billion dollar submarine deal with the UK and Australia, saying the security pact must fit its "America First" agenda.
Under the trilateral pact, believed to be aimed at countering China, Australia is to get its first nuclear-powered subs from the US, before the allies create a new fleet by sharing cutting-edge tech.
Both Australia and the UK – which did its own review last year – have played down news of the US probe, saying it is natural for a new administration to reassess.
The move comes as both Australia and the UK face pressure from the White House to lift military spending, demands heeded by Downing Street but largely resisted by Canberra.
The Aukus agreement – worth £176bn ($239bn; A$368bn) – was signed in 2021, when all three countries involved had different leaders.
A US defence official told the BBC the pact was being reviewed "as part of ensuring that this initiative of the previous administration is aligned with the President's America First agenda".
"As [US Defence] Secretary [Pete] Hegseth has made clear, this means ensuring the highest readiness of our servicemembers [and] that allies step up fully to do their part for collective defence," the defence official said.
The US has been pushing allies to start spending at least 3% of GDP on defence as soon as possible.
The UK has agreed to spend 2.5% of GDP on its defence by 2028, and 3% by the next parliament, while Australia has also said it will lift funding, but not to the 3.5% that the US wants.
The review will be headed up by Elbridge Colby, who has previously been critical of Aukus, in a speech last year questioning why the US would give away "this crown jewel asset when we most need it".
Defence Minister Richard Marles, speaking to local Australian media on Thursday morning local time, said he was optimistic the deal would continue.
"I'm very confident this is going to happen," he told ABC Radio Melbourne.
"You just need to look at the map to understand that Australia absolutely needs to have a long-range submarine capability."
Some in Australia have been lobbying for the country to develop a more self-reliant defence strategy, but Marles said it was important to "stick to a plan" – a reference to the previous government's controversial cancellation of a submarine deal with France in favour of Aukus.
An Australian government spokesperson told the BBC it was "natural" that the new administration would "examine" the agreement, adding the UK had also recently finished a review of the security pact between the long-standing allies.
There is "clear and consistent" support for the deal across the "full political spectrum" in the US, they said, adding Australia looked forward to "continuing our close cooperation with the Trump Administration on this historic project".
A UK defence spokesperson told the BBC it was "understandable" for a new administration to look at the deal, "just as the UK did last year".
Aukus is a "landmark security and defence partnership with two of our closest allies", the spokesperson said, and "one of the most strategically important partnerships in decades, supporting peace and security in the Indo-Pacific and Euro-Atlantic".
Jennifer Kavanagh, from American thinktank Defense Priorities, told the BBC that the US was "absolutely right to take another look at this deal" as its submarine capacities were already stretched.
"The US cannot meet its own demand for these nuclear-powered submarines," she said.
The other concern the US might have is whether Australia would use the submarines they buy in the way the US wants them to, she said, particularly if conflict erupts over Taiwan.
Dr Kavanagh said the review might see the security pact shift its focus away from providing submarines to sharing other long-range weapons technology.
However, if the US were to pull out of the deal, China would "celebrate" as they have long criticised the deal, Dr Kavanagh added.
What is Aukus?
For Australia, the deal represents a major upgrade to its military capabilities. The country becomes just the second after the UK to receive Washington's elite nuclear propulsion technology.
Such submarines will be able to operate further and faster than the country's existing diesel-engine fleet and Australia would also be able to carry out long-range strikes against enemies for the first time.
It is a big deal for the US to share what is often called the "crown jewels" of its defence technology.
But arming Australia has historically been viewed by Washington and Downing Street as essential to preserving peace in a region they themselves aren't a part of.