A multi-billion dollar submarine deal between long-standing allies - Australia, the UK and the US - has come under the spotlight after the Trump administration said it was reviewing how the deal fits in with its heavily-touted "America First" agenda.

LONDON (Reuters) -Britain said on Thursday it understood a decision by U.S. President Donald Trump's administration to launch a formal review into the AUKUS submarine pact, repeating London's position that the project was crucial to peace and security.

The United States Department of Defense officially announced a review of the AUKUS security deal on Wednesday, stating that it aims to ensure the initiative aligns with President Donald Trump's America First agenda.