U.S. Vice President Joe Biden urged Japan and China to lower tensions that have spiked since Beijing announced an air defense zone over disputed islands in the East China Sea, while repeating that Washington was "deeply concerned" by the move.
The United States has made clear it would stand by treaty obligations that would require it to defend the Japanese-controlled islands, but is also reluctant to get dragged into any military clash between the Asian rivals.
(Read more: China scrambles jets to new defense zone)
Biden will meet Japanese Prime Minister Shinzo Abe on Tuesday before flying to China the next day as part of an Asian trip in which he will seek a delicate balance between calming tensions over the zone while backing key ally Japan.
"We remain deeply concerned by the announcement of a new Air Defense Identification Zone," Biden said in written answers to the Asahi daily newspaper.
"This latest incident underscores the need for agreement between China and Japan to establish crisis management and confidence building measures to lower tensions."
Influential Chinese tabloid the Global Times, published by the Communist Party's official People's Daily, said Biden should not cozy up to Abe or offer effusive support to Japan.
"The only choice he has if he wants a successful trip (to China) is not to go too far in his words over there," it wrote in an editorial. "If he openly supports Tokyo and wants to 'send an expedition to punish' Beijing, the Chinese people won't accept it."
Japan reiterated on Tuesday that Tokyo and Washington had both rejected Beijing's move to set up the zone - despite the fact that three U.S. airlines, acting on government advice, are notifying China of plans to transit the area.
"We and the United States have the same stance of not recognizing this ADIZ," Chief Cabinet Secretary Yoshihide Suga told a news conference. "We firmly confirm this."
Washington said over the weekend that the advice to U.S. airlines did not mean U.S. acceptance of the zone, and last week sent two B-52 bombers into the area without informing China.
The Japanese and South Korean governments have advised their airlines not to submit flight plans in advance, which China has demanded from all aircraft since it announced the creation of the zone on November 23.
Angst at Japanese airlines
Japan Airlines and ANA Holdings, while complying with the government directive, are uneasy about flying through the zone without giving notice to China, especially after Washington advised U.S. carriers to comply, two sources familiar with the Japanese carriers' thinking told Reuters.
White House spokesman Jay Carney told a briefing that for safety reasons, U.S. carriers operated in accordance with notices issued by foreign countries.
"However - and let me be clear - this in no way indicates U.S. government acceptance of China's requirement in the newly declared ADIZ, and has absolutely no bearing on the firm and consistent U.S. government position that we do not accept the legitimacy of China's requirements," Carney said.
Washington takes no position on the sovereignty of the disputed 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.
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.
Biden dismissed doubts in Japan and elsewhere in the region over whether the United States has the resources to carry out a strategic "rebalance" that Washington says is a cornerstone of its foreign policy in Asia, given U.S. fiscal woes, its attention on the Middle East, and partisan battles at home.
Some experts said those doubts may have encouraged China to think the United States would not react strongly to its announcement of the air defense zone.
"Japan knows that we have stayed for more than 60 years, providing the security that made possible the region's economic miracle," he said.
"Economically, diplomatically, militarily, we have been, we are, and we will remain a resident Pacific power."