Secretary of State John Kerry and British Defense Secretary Chuck Hagel urged China to exercise restraint after Japan branded the move as "very dangerous".
China said it was setting up the "air defense identification zone" in the East China Sea that includes disputed islands administered by Tokyo to "guard against potential air threats".
"This unilateral action constitutes an attempt to change the status quo in the East China Sea. Escalatory action will only increase tensions in the region and create risks of an incident," Kerry said yesterday.
Hagel reiterated that the Japanese-administered Senkaku islands- which the Chinese claim and call the Diaoyu- fell under the US-Japan security treaty, meaning that Washington would defend its ally Tokyo if the area is attacked.
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"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 said.
"We view this development as a destabilising attempt to alter the status quo in the region. This unilateral action increases the risk of misunderstanding and miscalculations," Hagel said.
Japan last year nationalised the islands last year and has vowed not to cede sovereignty or even to acknowledge a dispute with China, accusing its growing neighbor of trying to change the status quo through intimidation.
China and Taiwan both claim the islands, which fall near potentially energy-rich waters.
"We remain steadfastly committed to our allies and partners, and hope to see a more collaborative and less confrontational future in the Pacific," Kerry said.