Japan reiterated on Monday that Tokyo and Washington had both rejected Beijing's move to set up an air defence 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 defence 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, whichChina 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 politicising" 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 recognises 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.


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