Tensions are starting to build in the Asia-Pacific with China’s recent establishment of an “Air Defense Identification Zone” in the East China Sea.

The zone, established Nov. 23, blankets most of the East China Sea, including a group of uninhabited islets whose ownership is disputed by China and Japan. The Chinese Defense Ministry says it will take “defensive emergency measures” against unidentified aircraft that fly into the area.

The Pentagon’s response was swift. “The United States is deeply concerned by the People’s Republic of China announcement today that it is establishing an Air Defense Identification Zone in the East China Sea,” Defense Secretary Chuck Hagel said on the same day China established the zone. “We view this development as a destabilizing attempt to alter the status quo in the region. This unilateral action increases the risk of misunderstanding and miscalculations.”

The U.S. is executing its Pacific pivot, a rebalancing of resources to the Asia-Pacific. While many American allies and partners in the region welcome the policy change, defense analysts have voiced concerns about the potential for conflict between U.S. and Chinese forces.

“This announcement by the People’s Republic of China will not in any way change how the United States conducts military operations in the region,” Hagel says. “The United States is conveying these concerns to China through diplomatic and military channels, and we are in close consultation with our allies and partners in the region, including Japan.”

“We remain steadfast in our commitments to our allies and partners,” Hagel says. “The United States reaffirms its longstanding policy that Article V of the U.S. Japan Mutual Defense Treaty applies to the Senkaku Islands.”

The islands have become a flashpoint for conflict between Japan and China, both of whom claim the region as their own.

Talking to reporters in an August press conference at the Pentagon, Gen. Chang Wanquan, China’s defense minister, underlined the Chinese stance. “We always insist that related disputes be solved through dialogue and negotiation,” he said. “However, no one should fantasize that China would barter away our core interests. And no one should underestimate our will and determination in defending our territory, sovereignty, and maritime rights.”

But Chang also adds that “the Asia-Pacific is our common homeland. Nations big or small, strong or weak, should make positive and constructive efforts for promoting regional peace and stability.”