“This is utterly irresponsible conduct,” Mr. Zhao said.
In Australia, the move was considered a momentous shift by some strategists. “The Australian decision to go this way is not just a decision to go for a nuclear-powered submarine,” said Hugh White, a professor at Australian National University and a former Australian defense official. “It’s a decision to deepen and consolidate our strategic alignment with the United States against China.”
He added, “This just further deepens the sense that we do have a new Cold War in Asia and that Australia is betting that in that new Cold War, the U.S. is going to emerge victorious.”
The announcement is the latest action in a U.S. strategy to push back on Chinese economic, military and technological expansion, carried out by Mr. Biden; his national security adviser, Jake Sullivan; and his Asia coordinator, Kurt Campbell. Over the past eight months, they have blocked China from acquiring key technologies, including materials for semiconductor production; urged nations to reject Huawei; edged toward closer dealings with Taiwan; and denounced China’s crackdown on Hong Kong.
Next week, Mr. Biden will gather the leaders of “the Quad” — an informal partnership of the United States, Japan, India and Australia — at the White House for an in-person meeting, another way to demonstrate common resolve in dealing with Beijing.
Mr. Biden spoke with President Xi Jinping of China last week for roughly 90 minutes, only the second time the two leaders have spoken in since Mr. Biden took office. Few details of the conversation were revealed, so it is unclear whether Mr. Biden gave his Chinese counterpart warning of the move with Australia. But none of it would have come as a surprise to Beijing; earlier, the Australians had announced a deal with France for less technologically sophisticated submarines. That deal collapsed.
Nonetheless, the decision to share the technology for naval reactors, even to a close ally, was a major move for Mr. Biden — one bound to raise protests by China and questions from American allies and nonproliferation experts. The United States last shared the nuclear propulsion technology with an ally in 1958 in a similar agreement with Britain, administration officials said.
“There is a shared understanding that we need to strengthen deterrence and actually be prepared to fight a conflict if one occurs,” said Bonnie Glaser, director of the Asia program at the German Marshall Fund, a policy think tank. “It reflects growing concern about Chinese military capabilities and intentions.”