TOKYO - In what was supposed to be a warm reunion, Vice President Biden and Chinese President Xi Jinping will meet instead Wednesday in a climate fraught with tension over an airspace dispute that has put Asia on edge. A day before seeing Xi, Biden stood in Japan and rebuked China for trying to enforce its will on its neighbors, escalating the risk of a potentially dangerous accident.

Although Biden had hoped to focus on areas of cooperation as the United States seeks an expanded Asia footprint, China's declaration of a new air-defense zone above disputed islands in the East China Sea has pitted the United States and China against each other, creating a wide gulf that Biden will seek to bridge during his two-day trip to Beijing.

Despite Washington's preference not to get involved in a territorial spat, concerns that China's action could portend a broader effort to assert its dominance in the region has drawn in the United States, putting Biden in the middle as he jets from Japan to China to South Korea on a weeklong tour of Asia.

"We, the United States, are deeply concerned by the attempt to unilaterally change the status quo in the East China Sea," Biden said after meeting in Tokyo on Tuesday with Japanese Prime Minister Shinzo Abe. "This action has raised regional tensions and increased the risk of accidents and miscalculation."

To that end, Biden said he would raise those concerns with China's leaders "with great specificity" during his Beijing visit.

Although the United States has repeatedly said it rejects the zone, Biden has avoided calling publicly for Beijing to retract it, wary of making demands that China is likely to snub. Rather, the United States hopes that with enough pressure, China will refrain from strictly enforcing the zone, essentially nullifying it for practical purposes.

What's more, the United States wants to show that the diplomatic consequences for such actions are severe enough that China will think twice in the future about asserting its authority in such heavy-handed ways. Already, China has claimed it has a sovereign right to establish a similar zone over the South China Sea, where China and the Philippines are locked in another long-running territorial dispute.

The East China Sea zone covers more than 600 miles from north to south above international waters separating China, South Korea, Japan, and Taiwan. China says all aircraft entering the zone must notify Chinese authorities beforehand or face unspecified defensive measures.

The new round of tensions with China comes as the United States is striving to increase its own engagement, influence and military presence in Asia, in part as a hedge against China's growing power. But the Obama administration has said it's pursuing a new model for engagement with China, where the two countries can cooperate economically while maintaining a healthy competition.

After an official welcome ceremony, Biden will meet with Vice President Li Yuanchao before his evening session with Xi.