The United States and Japan have announced an agreement for the return to Japan of a US air base, taking a step to resolving an issue that has vexed ties when both countries face a belligerent North Korea and a rising China.
The US Marines' Futenma air base on Okinawa island will be returned to Japan as early as 2022 if a planned relocation within the island is carried out.
By unveiling the deal, which includes time frames for the return of all or part of five other US military facilities on the southern Japanese island, Japan and the United States aim to send a message that their alliance is on a solid footing.
"With the security environment in the Asia-Pacific region getting tougher, I'm glad that we were able to show that the bond of trust in the Japan-US alliance is not wavering at all," Japanese prime minister Shinzo Abe told reporters.
Japan's ties with the United States were strained after then-prime minister Yukio Hatoyama in 2009 sought to keep a campaign promise to move the Futenma base off the island.
The Japanese government, however, could find no alternative site and was forced to reaffirm a 2006 agreement to move the base to a less populous area on the island, although the plan still faces opposition from residents, who associate US bases with noise, pollution and crime.
Okinawa, occupied by the United States from 1945-72, accounts for less than 1 percent of Japan's total land but hosts three-quarters of the US military facilities in the country in terms of land area.
The Futenma facility is surrounded by more than 100 schools, hospitals and shops. Former Japanese defence minister Naoki Tanaka once called it the world's most dangerous air base.
Mr Abe's government hopes to win the support of residents for the relocation of Futenma facility to another part of Okinawa.
The agreement comes when the United States is shifting its economic, diplomatic and security focus to Asia-Pacific.
"Now more than ever it is essential that the United States maintain a geographically distributed and sustainable force throughout Asia that can provide for the protection of Japan and our other allies, and US interests," US defense secretary Chuck Hagel said in a statement.
"We are resolved to focus our bilateral efforts on modernizing the alliance to meet emerging security challenges."
Osaka University professor Kazuya Sakamoto said the agreement would help maintain the deterrent that the Japan-US alliance posed.
"It is extremely dangerous to give out an impression the deterrent is weakening," he said.
Ties between China and Japan deteriorated sharply when Japan bought disputed East China Sea islets from a private Japanese owner last September.
The island row has in recent months escalated to the point where both have scrambled fighter jets while patrol ships shadow each other in nearby seas, raising worries that an unintended collision or other incident could lead to a broader clash.