The United States said Friday it would pull 9,000 Marines out of Japan as it seeks to ease a long-running standoff over the future of its huge military presence in one of its top Asian allies.
The redeployment will see the troops sent to Guam, Hawaii and Australia.
Withdrawing troops was originally part of plans to move a busy US airbase on Okinawa to another area of the southern island chain but US officials decided to separate the two issues due to ongoing opposition to the base relocation.
In a joint statement issued in Washington and Tokyo, the two sides said they remained committed to move the Futenma base from its present urban site to a coastal spot.
The relocation is being heavily resisted among many locals, who want to see the base moved out of Okinawa altogether.
The two governments "reconfirmed their view that (this) remains the only viable solution that has been identified to date", the statement said.
No definite timeframe was put on the redeployment, with the statement saying only that the "relocations are to be completed as soon as possible while ensuring operational capability throughout the process".
US Defense Secretary Leon Panetta hailed the deal, which he said would reduce the burden on residents of Okinawa.
"I am very pleased that, after many years, we have reached this important agreement and plan of action," Panetta said in a statement.
Japanese Foreign Minister Koichiro Gemba said the agreement reflected evolving regional realities, at a time of growing fears among Asian countries and the United States about China's increasing military might.
"Changes in the security environment will not wait for us. Japan and the United States have to assume our responsibility and do our part and implement the plans in a speedy manner," he told reporters in Tokyo.
"The (base-move) problem brought everything to a halt. We must make progress where we can."
The deal comes just ahead of a visit to Washington by Prime Minister Yoshihiko Noda, who will meet with President Barack Obama on Monday for what both sides hope will be a demonstration that the alliance is back on track.
Japan and the United States have long clashed over Okinawa, the site of sporadic tensions with US troops.
Around half of the 47,000 US service personnel in Japan are based on the strategically located island chain, which is nearer to Taiwan than it is to Tokyo.
The United States had agreed in 2006 to shift the Futenma air base -- a longtime source of grievance as it lies in a crowded urban area -- to a quiet stretch of seashore, with 8,000 Marines leaving Okinawa for Guam.
Some activists in Okinawa have pressed for the base to be removed completely and the controversy felled one Japanese prime minister, Yukio Hatoyama, who failed to fulfil campaign pledges in 2009 to renegotiate the deal.
Friday's announcement comes after the two sides said they would treat the marine redeployment as separate from the base move, which is likely to remain a matter of dispute.
A senior State Department official said the delinking had allowed things to move forwards.
"Previously everything was a package, until we had progress on constructing the Futenma replacement facility, we weren't doing a lot of other things," said the official, who requested anonymity, in line with usual policy.
"One of the key aspects of this agreement is that we're separating the piece of constructing a replacement facility for Futenma from the other aspects of the agreement because we're acknowledging it's taking more time than we anticipated."
The statement said the total cost of the relocation to Guam was expected to be $8.6 billion, with the US official saying more than a third would be paid by Tokyo.
Around 5,000 of those leaving Okinawa would be heading to Guam, with the remainder going to Hawaii and Australia where Washington is "establishing a US Marine Corps rotational presence", the statement said.
"In executing these moves, the US government reaffirmed its commitment to sustain its current military presence and enhance military capability in the Western Pacific."
The agreement is part of a wider US strategy under Obama, who is pushing to re-engage with Asia and reconfigure the American military presence in the region amid concerns over China's rapid rise.