British Prime Minister Boris Johnson on Thursday sought to play down Chinese fears that a deal to provide Australia with nuclear-powered US submarines threatened regional stability.

Johnson told parliament the move, part of a new defence alliance between Britain, Australia and the United States, was "not intended to be adversarial".

It "will help to safeguard the peace and security of the Indo-Pacific", he said, adding that the deal reflected "the close relationship that we have with the United States and with Australia, the shared values that we have and the sheer level of trust".

Britain in March unveiled plans to pivot its strategic focus towards Asia as part of the government's Integrated Review of foreign and defence policy.

The move follows the country's full departure from the European Union in January this year, and its efforts to forge closer trade ties with Asian countries.

Johnson acknowledged that the region was becoming "the geo-political centre of the world".

"If there was ever any question about Global Britain's tilt towards the Indo-Pacific... then this partnership with Australia and the US provides the answer," he said.

"It amounts to a new pillar of our strategy, demonstrating Britain's generational commitment to the security of the Indo-Pacific and showing exactly how we can help one of our oldest friends promote regional stability."

Johnson, his Australian counterpart Scott Morrison and US President Joe Biden announced the new defence pact -- AUKUS -- on Wednesday evening.

It has been seen as a demonstration of Western concern about China's growing influence in the region, and the pace and size of its military expansion.

- 'Cold War mentality' -

The president of the Beijing-based Center for China and Globalization think-tank, Henry Wang, told BBC radio the new defence alliance was "part of a Cold War mentality".

"I think there's a question over the purpose of setting up such an alliance in peacetime in the 21st century," he added.

Diplomatic ties between London and Beijing have been strained, notably over concerns about an authoritarian crackdown in Britain's former colony of Hong Kong.

This week, China's ambassador to London was banned from speaking to pro-Beijing lawmakers at parliament, after China sanctioned critical British MPs.

China has also been angered at British criticism of alleged human rights abuses against Uyghur Muslims in the Xinjiang region.

France called Australia's move to secure nuclear-powered subs from the United States "a stab in the back" after it abandoned a contract for diesel-powered subs.

British Defence Secretary Ben Wallace said London was not out to "antagonise the French" but accepted their frustration.

Wallace told the BBC television: "I understand France's disappointment... the Australians have taken this decision that they want to make a change.

"We didn't go fishing for that but as a close ally, when the Australians approached us, of course we would consider it. I understand France's frustration about it."

Wallace told Sky News separately France remained one of Britain's closest military allies, adding: "We have no intention of doing anything to antagonise the French."

"It's right that the UK, alongside other allies such as Australia stand up for the rules-based system and international law," he told the BBC.