The U.S. and Japan moved swiftly to warn China to refrain from escalating territorial tensions in the East China Sea, after Beijing stepped up the ante in its dispute with Tokyo by declaring a new air defense zone covering islands claimed by both nations.

Hours after China unveiled its new air defense identification zone, or ADIZ, on Saturday, warning of military action against foreign aircraft that don't honor its enforcement, U.S. Secretary of State John Kerry and Secretary of Defense Chuck Hagel sharply criticized China's action and reiterated Washington's commitments to defend Japan in case of a conflict.

The announcement from Beijing created an extensive area of overlap between Chinese and Japanese air defense zones, heralding a potentially dangerous new phase of the territorial dispute over the uninhabited Senkaku Islands, which are controlled by Japan but claimed by China and Taiwan, where they are known as Diaoyu.

A senior U.S. official said Sunday there would likely be a demonstration of American military resolve to continue operating in the area of the islands without Chinese interference.

The unspecified display isn't likely to involve a direct military confrontation. The senior official said there were no plans to immediately fly American planes into the expanded air defense identification zone, for instance.