US and Japanese leaders have vowed to deepen their post-World War II alliance to jointly tackle 21st century challenges, but analysts warn that a thorny row over military bases is far from over.
President Barack Obama made a point of starting his debut Asia tour on Friday in Japan, where he praised the half-century-old alliance as the "foundation of our security and prosperity" in Asia.
Obama and his host, centre-left Prime Minister Yukio Hatoyama, highlighted the shared goals of their Democratic parties and vowed to cooperate on climate change and work towards the goal of a world free of nuclear weapons.
The US president reassured Tokyo that, despite the rise of China, the United States values Japan for its democratic system, which saw Hatoyama elected in a landslide in August after decades of conservative rule.
Both nations, Obama said, believe in the people's right "to choose their own leaders and realise their own dreams, a belief that made possible the election of both Prime Minister Hatoyama and myself on the promise of change."
But for all the upbeat summit talk between the two relatively new leaders, they agreed to defer for now a dispute over what is a red-line issue for both -- what to do with plans for a new American airbase in Japan.
Hatoyama has rattled Washington by saying he is reviewing an agreement to build the new base on southern Okinawa island, where residents have long complained of the heavy post-World War II American military presence.
Defying US pressure to stick with the 2006 pact to close one base but build the replacement facility, the premier has maintained that Japan may decide instead to move the base off the island, perhaps even out of the country.
Hatoyama said that while Tokyo takes seriously the previous bilateral agreement the proposal to scrap the base deal "has heightened the expectations of the Okinawan people."
Obama said he wanted both sides to "expeditiously" settle the row about the planned relocation of the Marine Corps Futenma Air Station within Okinawa -- an island strategically located near China, Taiwan and North Korea.
He reminded Japan that its miracle rise from the ashes of war to become the world's number two economy was achieved while the US military guaranteed the security of the declared pacifist nation.
America's treaty alliances with Japan and other Asian countries, Obama pointedly said, "are not historical documents from a bygone era, but abiding commitments to each other that are fundamental to our shared security."
Japan experts said the base issue will remain a tough nut to crack.
Shinichi Nishikawa, a Meiji University politics professor, said "Obama truly wants to seal better relations with Japan. But the future of their relations will fully depend on how Japan can settle the base issue.
"If Tokyo fails to resolve the problem, the friendly atmosphere can easily evaporate. There still is a gap between the two countries. It's as if they are in the same bed but dreaming different dreams."
Former Pentagon official James Shinn, now a Princeton University lecturer, said Japan had focused on domestic issues at the expense of the larger security picture, including North Korea.
Amid the haggling over land, he said, he was astonished "how little time and energy is spent on the serious security threats to Japan, with a nuclear-armed neighbour just a few tens of kilometres across the Sea of Japan."
Patrick Cronin, of the US Center for a New American Security, said "the relationship is in trouble but not yet in crisis" and predicted the United States may ultimately need to soften its position.
Cronin said the United States has valid reasons to want to keep Futenma's air operations on Okinawa, in case of a crisis in the region.
"But if the Japanese government says 'listen, we represent the people of Japan and we have to do something different,' we're going to have to listen to them," said Cronin.