"We agree that the PRC is the greatest shared strategic challenge that we and our allies and partners face," US Secretary of State Antony Blinken said after he and Defense Secretary Lloyd Austin met their Japanese counterparts in Washington, referring to the People's Republic of China.
At the same news conference on Wednesday, Austin announced plans to introduce a Marine Littoral Regiment in Japan, which would bring significant capabilities, including anti-ship missiles.
Blinken also said that two sides had agreed to extend the terms of their common defence treaty to cover space.
Austin is to meet Japanese Defence Minister Yasukazu Hamada again on Thursday at the Pentagon; afterward there will be a meeting between US President Joe Biden and Japanese Prime Minister Fumio Kishida on Friday.
Although the total number of US troops in Japan will not change, the new deployments could be the first of several announcements this year on military forces in Asia aimed at making Beijing think twice before initiating any conflict.
The agreement follows nearly a year of talks and comes after Japan last month announced its biggest military build-up since World War II - a dramatic departure from seven decades of pacifism, fuelled by concerns about Chinese actions in the region.
That five-year plan will double the country's defence spending to two per cent of its gross domestic product and see Japan procure missiles that can strike ships or land-based targets 1000 kilometres away.
Asked about the Japanese reforms, Blinken said: "It's very simple, we heartily welcome the new strategies especially because there is ... a remarkable convergence between our strategy and strategies and Japan's.
"We applaud the commitment to increase investment, to enhanced roles, missions and capabilities ... to closer cooperation not only between the United States and Japan but as well with other allies and other partners," he said. "We already have a strong foundation that's only going to grow."
The anti-ship missiles will arrive in Japan under a revamped Marine Corps regiment of 2000 troops that will focus on advanced intelligence, surveillance and transportation, US officials told Reuters. The move is expected to be completed by 2025.
The officials added that a separate US Army company of about 300 soldiers and 13 vessels would be deployed by this spring to help transport US and Japanese troops and equipment, allowing for the rapid dispersal of forces.
Japan has watched with growing concern China's belligerence toward Taiwan as Beijing seeks to assert its sovereignty claims over the island.
Austin noted ramped-up Chinese military activities near the Taiwan Strait, but said he seriously doubted they were a sign of plans for an imminent invasion of the island by Beijing.
