United States and Japanese officials say they will position a second early-warning radar in Japan within the next year and deploy new long-range surveillance drones to help monitor disputed islands in the East China Sea, moves that may raise tensions with China.
The foreign and defence ministers of the two countries also, for the first time, put a price on what Japan will contribute to the relocation of marines out of Okinawa to Guam and other locations in the Asia-Pacific region. Japan will pay up to US$3.1 billion ($3.7 billion) of the move, which includes development of facilities in Guam and the Northern Mariana Islands.
The announcements came at the close of high-level meetings between US Secretary of State John Kerry and US Defence Secretary Chuck Hagel with Japanese Foreign Minister Fumio Kishida and Defence Minister Itsunori Onodera. The talks, ahead of President Barack Obama's visits to Indonesia and Brunei next week, were aimed at modernising the American-Japanese alliance.
The new X-band radar system would boost Japan's ability to track and intercept missiles from across the Sea of Japan and will be set up on the west coast.
Officials have said it is aimed at protecting against the threat from North Korea, and is not directed at China. But the drones - two or three that will fly out of a US base - are designed in part to help step up surveillance around the Senkaku islands, a source of heated debate between Japan and China. The territorial dispute over the islands has badly soured China-Japan relations.
China has increased patrols near the Japanese-administered islands that it calls Diaoyu.
The cat-and-mouse between their ships and aircraft continues, and Beijing and Tokyo aren't even close to settling their dispute.
Successive US administrations have held to the position that the two nations must sort out their differences over the Senkakus peacefully.
A senior US official travelling with Kerry said Washington would continue to make the point that while it takes no side on the question of the islands' sovereignty, it recognises Japan's administration of them and has responsibilities to protect Japanese territory under a mutual defence treaty.
The islands, also claimed by Taiwan, stir a depth of nationalist passion that belies their size and remoteness. They are located roughly midway between Taiwan and the southern Japanese island of Okinawa, and cover a total area of just 5.9sq km.
Over the past year, Japan's coastguard says there have been more than 200 intrusions by foreign vessels into Japanese-claimed waters near the islands. The closest call came in February, when Japan said a Chinese ship locked its weapons fire-control radar on to a Japanese ship in a hostile act. China denied it.
A senior US Administration official said the new radar would provide better coverage in the event of a North Korean attack. There is already one of the X-band radar systems in the northern part of Japan, but the official said the second one, to be located in the Kyoto Prefecture, would fill gaps in coverage.