The United States has voiced its "strong concern" to China over threats from Beijing to enforce its claims to a set of disputed Pacific islands controlled by Japan but claimed by the People's Republic.
The White House, State Department and Pentagon all issued statements late Saturday, hours after Beijing threatened to take "defensive emergency measures" against aircraft entering its newly-proclaimed air defense zone. The Chinese edict called on all aircraft to identify themselves before entering the zone, and to obey all orders from Beijing.
The White House called the threat an escalatory development," while Defense Secretary Chuck Hagel called it "a destabilizing attempt to alter the status quo" in the East China Sea. Hagel also said the United States has no plans to change how it conducts military operations in the region.
The islands, known as Senkaku in Japan and Daioyu in China, are uninhabited, but surrounded by rich fishing grounds and potential energy deposits.
Earlier Saturday, Japan lodged a strong protest with Beijing that called establishment of the zone "totally unacceptable." Senior Japanese diplomat Junichi Ihara also criticized China for escalating bilateral tensions over the islands.
In the Chinese statement, which appeared Saturday on a defense ministry website, Beijing said the new rules were effective immediately.
After months of escalating tensions, Japan scrambled fighter jets earlier this month over the East China Sea, after it spotted what it said was an unmanned aircraft flying toward Japan.
Japan annexed the islets in the late 19th century. China claimed sovereignty over the archipelago in 1971, saying ancient maps show it has been Chinese territory for centuries.
The festering China-Japan dispute is one of several maritime controversies pitting China against several Southeast Asian nations, including the Philippines, Vietnam, Brunei and Malaysia.
Beijing has indicated a willingness to negotiate the disputes, but has so far rejected calls for multilateral talks. It has sought separate negotiations with each country.
Some information for this report was provided by AP and Reuters.