Revamping the guidelines of their defence partnership for the first time in 16 years, the allies agreed to position a second early-warning radar in Japan within the next year to help protect against North Korea.
And by next spring, they will deploy new long-range surveillance drones to help monitor disputed islands in the East China Sea, a move that may well raise tensions with Beijing.
Japan will pay up to USD 3.1 billion of the move, which includes development of new facilities in Guam and the Northern Mariana Islands.
US Secretary of State John Kerry and US Defence Secretary Chuck Hagel met with Japanese Foreign Minister Fumio Kishida and Defence Minister Itsunori Onodera and afterward laid out the details of the session.
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The talks, ahead of President Barack Obama's visits to Indonesia and Brunei next week, were aimed at modernising the American-Japanese alliance that both sides maintain is a cornerstone of peace and stability in North Asia.
The deep neighbourhood divisions were underscored, even as the meeting went on, when a new naval exercise between the US, Japan and South Korea scheduled for next week was disclosed, provoking a swift response from North Korea.
In a statement, the National Peace Committee of Korea condemned the exercise, which will include the USS George Washington aircraft carrier and its strike group, as reckless saber-rattling.
Officials have stressed it is not directed at China. Kerry acknowledged the threat from Pyongyang, but also said the US was willing to sign a non-aggression pact with North Korea if it gives up its nuclear weapons and complies with international demands.