US Vice-President Joe Biden is caught between some rocks and a hard place as he visits Asia this week.
Biden arrives in Beijing today with the difficult task of conveying the concerns of regional allies and defusing tensions over China's newly declared air defence identification zone, which includes the disputed rocky islets known as the Diaoyus in China and the Senkakus in Japan.
This is no easy job. Influencing Beijing has become increasingly difficult for the US, given their fundamentally different views on China's sovereignty issues. Reaffirming US commitment to the region could prompt demands from allies for a tougher stance on China, and that could reinforce Beijing's perception that it is being targeted for containment.
"He [Biden] has the tough task of striking a balance between trying to keep the relationship with China on an even keel while also reassuring US allies about Washington's planned future engagement in the region, after the cancellation of President [Barack] Obama's trip," said Stephanie Kleine-Ahlbrandt, Asia Pacific director at the US Institute of Peace, referring to the US president's no-show at two regional summits in October.
As the territorial dispute between Beijing and Tokyo over the islands escalates, the US diplomatic tightrope is getting tauter. Washington was quick to defy the air defence zone by sending two B-52 bombers to the area three days after the zone's establishment.
But Washington said on Friday that US civilian aircraft were expected to observe China's rules in the zone. Although the US said this did not mean it accepted China's requirements in the zone, it prompted criticism in Japan.
Tokyo, some experts said, expected Washington to be tougher on Beijing.
"Japanese are concerned about the US' total China policy, and if the US' inconsistent message to China might give the wrong impression to the Chinese, as Japan's [former] prime minister [Naoto] Kan did," said Hiroko Maeda, a research fellow with the Centre for International and Strategic Studies PHP Institute.
Maeda was referring to a clash between a Chinese fishing boat and two Japanese coastguard patrol vessels that developed into a diplomatic row in 2010 while Kan was prime minister. Japan's initial tough stance was later softened due to concerns about Japanese business interests in China. This gave China the impression that "Japan is weak", the academic said.
But for Washington, advancing its relationship with Beijing is also important. A White House official said last week that Biden was not travelling to Beijing to deliver a diplomatic démarche but to engage in dialogue over a wide range of shared interests.
"The Japanese of course don't want the US and China to be too close, to be colluding. But what the US is seeking to do is shape China's rise, to influence China as it becomes a bigger power," said Bonnie Glaser, a senior adviser for Asia at the Centre for Strategic and International Studies.
Influencing China, however, has become challenging, Glaser said. The US has limited leverage, and "it has to be careful how it uses it", Glaser said.
For Beijing, Washington's disagreement on China's territorial claims in the South and East China seas remains a major obstacle to bilateral relations, said Tao Wenzhao , a senior researcher with the Institute of American Studies at the Chinese Academy of Social Sciences.
The divergent views on territorial and sovereignty issues in the two seas, which Beijing has occasionally described as a core interest, have prevented Obama from wholly embracing what President Xi Jinping proposed as "a new type of major power relationship", according to Glaser.
The concept of this "new type" relationship was proposed by Xi in a meeting with Obama at the Sunnylands summit in the US last year before he became president. One element in this concept is for both sides to respect each other's core interests, something that Obama does not endorse.
"This [associating the two seas as a core interest] suggests they are so vital that China would be willing to go to war over them. The US is not willing to cede these issues to China," Glaser said.
What both leaders have agreed on, Glaser said, was the "sort of negative definition" on what the bilateral relationship should not be: that the two countries should avoid conflict and confrontation and try to manage their differences.
"When they try to come up with a more positive definition, of what it should be, that's really where the US and China diverge substantially," Glaser said.