The United States on Wednesday announced the launch of a security partnership with Britain and Australia in an apparent effort to counter China's assertiveness, paving the way for Canberra to obtain nuclear-powered submarines and join a handful of countries that operate them.

"We're taking another historic step to deepen and formalize cooperation among all three of our nations because we all recognize the imperative of ensuring peace and stability in the Indo-Pacific over the long term," President Joe Biden said at the White House, with his British and Australian counterparts attending virtually.

The latest development comes as Britain is stepping up its engagement in the region such as through the deployment of its aircraft carrier Queen Elizabeth, while Australia and China have seen their relations increasingly sour over disputes on trade and other issues.

China expressed its objection to the move, with a spokesman at the embassy in the United States saying in a statement that the three countries "should not build exclusionary blocs targeting or harming the interests of third parties."

In Beijing, Chinese Foreign Ministry spokesman Zhao Lijian on Thursday criticized the cooperation between the United States, Britain and Australia on nuclear-powered submarines for "seriously threatening regional peace and stability."

A Biden administration official insisted that the partnership named "AUKUS" -- representing the names of the three countries -- is not aimed at any specific country but is about advancing the group's strategic interests, upholding the international rules-based order and promoting peace and stability in the Indo-Pacific.

"This is meant to complement ongoing and existing security and political partnerships, and it's meant to send a message of reassurance and a determination to maintain a strong deterrent stance into the 21st century," the official said.

Under the new partnership, the three countries will promote deeper information and technology sharing and enhance joint defense capabilities and interoperability, with its initial focus set on cybersecurity, artificial intelligence and quantum technologies.

The first initiative will feature an 18-month effort to identify an "optimal pathway" for Australia to acquire nuclear submarines for its navy, according to a statement issued by the leaders.

In a separate statement, the Australian government said it envisions the delivery of "at least eight" such submarines as part of that effort.

The U.S. official highlighted the significance of sharing with Australia "extremely sensitive" nuclear propulsion technology, saying Britain is the only other country privy it, with the arrangement dating back to 1958.

Submarines powered by a nuclear reactor will enable Australia to deploy the vessels for longer periods and are quieter and more capable.

Australian Prime Minister Scott Morrison emphasized in his remarks that his country "is not seeking to acquire nuclear weapons, or establish a civil nuclear capability."

"And we will continue to meet all our nuclear nonproliferation obligations," he said.

British Prime Minister Boris Johnson said "it is a momentous decision for any nation to acquire the formidable capability" of possessing nuclear-powered submarines "and perhaps, equally momentous, for any other state to come to its aid."

"But Australia is one of our oldest friends, a kindred nation and a fellow democracy, and a natural partner in this enterprise," he said.

A total of six countries -- the United States, Russia, Britain, France, China and India -- are known to have nuclear-powered submarines, according to experts. They are all nuclear-armed countries.

According to a 2020 U.S. Defense Department report on China's military power, the People's Liberation Army Navy was operating six nuclear-powered attack submarines, and 50 diesel-powered attack submarines.

AUKUS, which the three countries say will also aim to foster deeper integration of industrial bases and supply chains, is the latest multilateral framework the Biden administration is pushing for amid its increasing competition with China in areas including the military, economy and technology.

"We undertake this effort as part of a larger constellation of steps, including stronger bilateral partnerships with our traditional security partners in Asia -- Japan, South Korea, Thailand, the Philippines -- and also stronger engagement with new partners like India, Vietnam, and new formations like the Quad," the U.S. official said.

The Quad is a group of major Indo-Pacific democracies involving the United States, Japan, Australia and India, and is seen as a counterweight to China's increasing clout. The Quad is scheduled to hold its first in-person meeting among the leaders of the four countries next week at the White House.