LONDON, Apr. 7 (Reuters) - The U.S., Britain and Australia are set to begin talks on bringing new members into their AUKUS security pact as Washington pushes for Japan to be involved as a deterrent against China, the Financial Times reported.

The countries' defence ministers will announce discussions on Monday on "Pillar Two" of the pact, which commits the members to jointly developing quantum computing, undersea, hypersonic, artificial intelligence and cyber technology, the newspaper reported on Saturday, citing people familiar with the situation.

They are not considering expanding the first pillar, which is designed to deliver nuclear-powered attack submarines to Australia, the FT said.

AUKUS, formed by the three countries in 2021, is part of their efforts to push back against China's growing power in the Indo-Pacific region. China has called the AUKUS pact dangerous and warned it could spur a regional arms race.

U.S. President Joe Biden has sought to step up partnerships with U.S. allies in Asia, including Japan and the Philippines, amid China's historic military build-up and its growing territorial assertiveness.

Rahm Emanuel, the U.S. ambassador in Tokyo, wrote in an opinion piece, opens new tab in the Wall Street Journal on Wednesday that Japan was "about to become the first additional Pillar II partner".

A senior U.S. administration official told Reuters on Wednesday that some sort of announcement could be expected in the coming week about Japan's involvement but gave no details.

Biden and Japanese Prime Minister Fumio Kishida will likely discuss expanding AUKUS to include Japan when the president hosts the prime minister in Washington on Wednesday, a source with knowledge of the talks said.

Australia, however, is wary of beginning new projects until more progress has been made on supplying Canberra with nuclear-powered submarines, said the source, who asked not to be identified because they are not authorised to speak to the media.

A spokesperson for the White House National Security Council and China's foreign ministry did not immediately respond to requests for comment on the FT report.

A Japanese foreign ministry spokesperson said the ministry could not immediately comment.

Australian Defence Minister Richard Marles has said they would "seek opportunities to engage close partners in AUKUS Pillar II" and any involvement of more countries would be decided and announced by the three partners, a spokesperson from his office said.

Britain's defence ministry said it too would like to involve more allies in this work, subject to joint agreement.

While the U.S. is keen to see Japanese involvement in Pillar Two, officials and experts say obstacles remain, given a need for Japan to introduce better cyber defences and stricter rules for guarding secrets.

U.S. Deputy Secretary of State Kurt Campbell, an architect of U.S. Indo-Pacific policy, said on Wednesday the U.S. was encouraging Japan to do more to protect intellectual property and hold officials accountable for secrets. "It's fair to say that Japan has taken some of those steps, but not all of them," he said.

The United States has long said that other countries in Europe and Asia are expected to join the second pillar of AUKUS.

The senior U.S. official said any decisions about who would be involved in Pillar Two would be made by the three AUKUS members, whose defence ministers had been considering the questions for many months, based on what countries could bring to the project.

Campbell said that other countries, opens new tab had expressed interest in participating in AUKUS.

"I think you'll hear that we have something to say about that next week and there also will be further engagement among the three defence ministers of the United States, Australia, and Great Britain as they focus on this effort as well," Campbell told the Center for a New American Security think tank.

Campbell also said on Wednesday the AUKUS submarine project could help deter any Chinese move against Taiwan, the democratically governed island that Beijing claims as part of China.

Biden, Kishida and Philippine President Ferdinand Marcos Jr are to hold a trilateral summit on Thursday.v