The United States "deeply concerned" and committed to defending its close ally Japan after China unilaterally decided to establish an air defense zone in the disputed East China Sea, Secretary of State John Kerry has said.
"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.
"We urge China not to implement its threat to take action against aircraft that do not identify themselves or obey orders from Beijing," Kerry said on Saturday in Geneva.
Kerry and British Defense Secretary Chuck Hagel also urged China to exercise restraint after Japan branded the move as "very dangerous".
China on Saturday 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". Beijing also scrambled air force jets to carry out a patrol mission in the newly declared zone.
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.
"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.
"The US 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," he 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.