The move is likely to alarm Australia, which sees the submarines as critical to its defence as tensions grow over China’s military build-up

US President Donald Trump’s administration has launched a formal review of a defence pact worth hundreds of billions of dollars that his predecessor Joe Biden made with Australia and the United Kingdom, allowing Australia to acquire conventionally armed nuclear submarines, a US defence official said.

The formal Pentagon-led review is likely to alarm Australia, which sees the submarines as critical to its own defence as tensions grow over China’s expansive military build-up.

It could also throw a wrench in Britain’s defence planning. The Aukus security alliance is at the centre of a planned expansion of its submarine fleet.

“We are reviewing Aukus as part of ensuring that this initiative of the previous administration is aligned with the president’s America First agenda,” the official said of the review, which was first reported by the Financial Times.