The United States says it’s “deeply concerned” and committed to defending Japan, with China announcing an air zone in the East China Sea that includes disputed islands.

In a move that US ally Japan has branded as “very dangerous,” China says it’s setting up the “air defence identification zone” over the islands administered by Tokyo to “guard against potential air threats”.

In similar statements, Secretary of State John Kerry and Secretary of Defense Chuck Hagel said on Saturday the United States was “deeply concerned” about the moves by China, which also scrambled air force jets to patrol the newly declared zone.

“This unilateral action constitutes an attempt to change the status quo in the East China Sea,” Kerry said.

“Escalatory action will only increase tensions in the region and create risks of an incident,” the top US diplomat said from Geneva, where he was taking part in talks on reaching an agreement with Iran on its nuclear program.

Kerry said the United States was urging China to “exercise caution and restraint”, and warned Beijing against implementing its new 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 Washington would defend 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.

The defence chief made clear the US, which stations more than 70,000 troops in Japan and South Korea, would not respect China’s declaration of control over the zone.

The outline of the zone, which is shown on the Chinese defence ministry website and a state media Twitter account, covers a wide area of the East China Sea between South Korea and Taiwan that includes airspace above the disputed islands.

Japan last year nationalised the islands and has vowed not to cede sovereignty or even to acknowledge a dispute with China, accusing its growing neighbour of trying to change the status quo through intimidation.

China and Taiwan both claim the islands, which fall near potentially energy-rich waters.