Adding partners to the AUKUS defense project would be "complicated," a senior Australian diplomat said Friday, saying he did not believe the U.S. Congress is open to expanding the pact involving Australia, the U.S. and Britain.

AUKUS was formed in 2021 to counterbalance China's growing power. A first "pillar" involves cooperation between the three partners to provide Australia with nuclear-powered submarines, but they have raised the possibility of other countries joining a second pillar to develop other high-tech weaponry.

Paul Myler, deputy head of mission at Australia's Embassy in Washington, said that it was an "almost inconceivable" achievement that after 40 years of effort to reform U.S. export control restrictions, the partners were on the verge of creating an environment for easier collaboration and co-development.