The US has taken a major step towards implementing the AUKUS security pact by signing on to an estimated $US2 billion ($A3 billion) training-and-equipment agreement.

AUKUS is a trilateral defence technology partnership between the United States, the United Kingdom and Australia.

“Australia is one of our closest, most trusted, and capable global allies, committed to ensuring peace, security, and stability in the Indo-Pacific region and beyond,” the US State Department said in a statement on Friday.

“The US-Australia alliance is critical to US national interests, and the United States has a long history of working with Australia to develop and maintain strong defense capabilities.

“The proposed sale of this equipment and support will not alter the basic military balance in the region and serves to promote a free and open Indo-Pacific region that is secure and stable in line with US national security, foreign policy, and defence goals.”

Meanwhile, US Secretary of Defence Lloyd J. Austin III, Australia’s Defence Minister Richard Marles and UK Secretary of State for Defence Grant Shapps gathered in California on Friday to discuss AUKUS.

They agreed the security agreement was a generational opportunity to modernise and enhance longstanding partnerships and cooperation, to address global security challenges, and contribute to stability and prosperity in the Indo-Pacific region “and beyond”.

“For Australia’s acquisition of conventionally armed, nuclear-powered submarines, AUKUS partners are collaborating to deliver this capability at the earliest possible date while upholding the highest nuclear non-proliferation standard,” they said in a joint statement.

The deal has been the subject of reservations by some on Capitol Hill who argue US defence needs will come under pressure as shipyards turn to Australia’s new submarine fleet.

-AAP