US Vice President Joe Biden has his work cut out for him in Asia. He left for a tour of Japan, China and South Korea on Sunday.

On his trip, Biden will seek to calm tensions between China and Japan, while reassuring Japan of the United States’ support in the territorial dispute over islands in the East China Sea.

The White House said Biden’s trip would also emphasize Washington’s “enduring presence as a Pacific power… and underscore our commitment to rebalancing US foreign policy towards the Asia-Pacific.”

On Monday, Japan reiterated that both Tokyo and Washington rejected China’s air defense identification zone in the East China Sea, which includes the disputed Senkaku islands (known as Diaoyu in China).

More from GlobalPost: War between Japan and China is an accident waiting to happen

“The US 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 said during a news conference.”

Three American airlines plan to notify China of their flight plans, upon advice from the government. However, Washington said this did not indicate acceptance of the air defense zone.

Japanese Prime Minister Shinzo Abe plans to discuss the matter with Biden in Tokyo.

Japan’s airlines will not submit their flight plans to China, upon the Japanese government’s request.

“The prospect of a planned war between these two countries is slight,” Dr. John Lee, an expert on energy security at the University of Sydney, told GlobalPost in November. “But the prospect of an unintended escalation, stemming from an incident at sea is significant.”

The United States has no stance on the islands, but acknowledges Japan’s administrative control over them. In case the issue ended in military conflict, Washington would come to Tokyo’s aid.

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