By Kiyoshi Takenaka and David Brunnstrom
TOKYO/WASHINGTON (Reuters) - U.S. Vice President Joe Biden will seek a delicate balance between calming military tensions with China and backing ally Japan against Beijing on a trip to Asia this week that is being overshadowed by a territorial row in the East China Sea.
Japan reiterated on Monday that Tokyo and Washington had both rejected Beijing's move to set up an air defense zone that includes islands at the heart of a bitter Sino-Japanese feud - despite the fact that three U.S. airlines, acting on government advice, are notifying China of plans to transit the zone.
Washington said over the weekend this did not mean U.S. acceptance of the zone, and last week sent two B-52 bombers into the area without informing China.
"The U.S. government has made it clear that it is deeply concerned about China's establishment of the air defense identification zone, and that it will not accept China's demands regarding operations in the zone," Japanese Chief Cabinet Secretary Yoshihide Suga told a news conference.
Japan's two biggest airlines are following a request from their government not to submit flight plans in advance, which China has demanded from all aircraft since it announced the creation of the zone last month.
South Korean authorities have also advised the country's airlines not to submit flight plans to China for flying through the zone, which overlaps with a submerged rock claimed by Beijing and Seoul.
Chinese Foreign Ministry spokesman Hong Lei said China appreciated the United States urging its airlines to notify China of flight plans, but chastised Japan for "deliberately politicizing" the issue.
Sino-Japanese ties, often fraught due to regional rivalry, mutual mistrust and bitter Chinese memories of Japan's wartime occupation, have become increasingly acrimonious because of a quarrel over tiny islands claimed by both Tokyo and Beijing.
In Tokyo on Tuesday, Biden will likely assure Japan that a military alliance with the United States dating back to the 1950s remains valid as the government of Prime Minister Shinzo Abe wrangles with China over the islands.
Yet, he will also try to calm tensions between the United States and key trade partner China over the same territorial dispute when he goes to Beijing later in the week.
"It's especially important ... that we continue to amplify our messages that we are and always will be there for our allies, and that there is a way for two major powers in the U.S. and China to build a different kind of relationship for the 21st century," a senior Obama administration official said.
Washington takes no position on the sovereignty of the islands, known as the Senkaku in Japan and the Diaoyu in China. However, it recognizes Tokyo's administrative control and says the U.S.-Japan security pact applies to them, a stance that could drag the United States into a military conflict it would prefer to avoid.
U.S., Japanese and South Korean military aircraft all breached the zone last week without informing Beijing and China later scrambled fighters into the area.
Other countries including the United States, Japan and South Korea have similar zones but only require aircraft to file flight plans and identify themselves if those planes intend to pass through national airspace.
FEARS OF CLASH
The military posturing has raised fears of a clash between the United States and its allies and China as it becomes more assertive in the East China Sea and South China Sea under President Xi Jinping.
The U.S. Navy's first advanced Poseidon patrol aircraft arrived on Japan's southern island of Okinawa on Sunday, the start of a previously planned deployment that will upgrade America's ability to hunt submarines in seas close to China.
Some experts said China may have overreached with its announcement of the air defense zone, and Biden is expected to suggest ways out of the crisis when he meets Xi in Beijing on Wednesday.
"What the Americans can hope to do is to try to tell the Chinese that this ratcheting up is not very clever and is counterproductive and that there is a way out, which is for the Chinese simply to de-emphasize (the defense zone) and not to enforce it," said Jonathan Eyal, director of international security studies at the Royal United Services Institute in London.
Experts said the gap in the two allies handling of commercial flights in China's new zone, while unwelcome in Tokyo, reflected a difference in the degree to which national interests were at stake.
"After all, because the line is over the Senkakus, Japan is a much closer interested party," said Akio Takahara, a professor at the University of Tokyo.
"Of course the zone overlaps the U.S. training area and they're very angry about this, but they have a bit of leeway that Japan doesn't. It has the geographical distance and the level of its military superiority is different."
Few foresee a quick resolution to the air defense zone dispute. "China will probably say to Biden that this is a standard practice for more than 20 countries. Why the fuss?" said Jia Qingguo, professor and associate dean of the School of International Studies at Peking University.
"It is helpful for the two sides to gauge each other's intentions and clarify issues and develop some kind of understanding as to what to expect. But this issue will probably linger on," Jia said.
Despite the standoff, U.S. officials see increased cooperation on a range of issues from climate change to North Korea's nuclear weapons ambitions.
It is unclear whether Biden will ask for Chinese help in pressuring North Korea to release U.S. war veteran Merrill Newman, 85, who it arrested last month.
(Additional reporting by Michael Martina and Megha Rajagopalan in Beijing and Elaine Lies in Tokyo; Writing by Alistair Bell and Linda Sieg; Editing by Vicki Allen, Eric Walsh, and Dean Yates)