U.S. Secretary of Defense Lloyd Austin delivering his speech at a plenary session of the International Institute for Strategic Studies (IISS) 21st Shangri-La Dialogue in Singapore, June 1, in a handout photo made available by the U.S. Department of Defense. EPA-Yonhap

The United States is unlikely to help Korea build nuclear-powered submarines at the moment, as it is stretched by AUKUS commitments to Australia, U.S. Defense Secretary Lloyd Austin said at the Shangri-La security dialogue in Singapore.

In 2021 the United States signed the AUKUS pact with Britain and Australia to share nuclear-powered submarine technology and to sell at least three Virginia-class boats to Australia in the 2030s.

Several other allies, including Korea, have expressed interest in involvement.

Asked on Saturday at the security summit how he would respond to a direct Korean request for help obtaining nuclear submarines, Austin said it would be "very, very difficult" for Washington to accommodate that "on top of what we do right now."

"(AUKUS) is no small endeavour," he said. "We just started down this path with Australia. (It's) highly doubtful that we could take on another initiative of this type anytime in the near future."

The two-stage security pact aims to counteract China's growing power in the Asia-Pacific region. It will be the first time Washington has shared nuclear-propulsion technology since it did so with Britain in the 1950s.

It includes a second technology-sharing "pillar," besides the submarines, which has drawn interest from New Zealand and Japan.

"We believe that AUKUS is actually a good addition to regional security," New Zealand Defence Minister Judith Collins said on the sidelines of the Shangri-La Dialogue on Friday, adding that New Zealand had enquired about the second pillar

"We've had no actual invitation to join it but it is something that we are certainly looking at," she said.

Australian Defence Minister Richard Marles said that he could imagine other countries' involvement in the future but that the focus for now was on the U.S.-UK-Australia trio getting "runs on the board" of submarine projects, which are set to last decades. (Reuters)