China has declared an "air-defense identification zone" over an area of the East China Sea, covering islands that are also claimed by Japan. The islands are known as Senkaku in Japan and Diaoyu in China.
China said Saturday that noncommercial aircraft entering a broad zone over the East China Sea must first identify themselves to Beijing, at the risk of facing “defensive emergency measures” by Chinese armed forces. Japan lodged a strong protest over what it said was an "escalation," and experts said that the risk of a military confrontation between the countries has grown.
"Setting up such airspace unilaterally escalates the situations surrounding Senkaku islands and has danger of leading to an unexpected situation," Japan's foreign ministry said in a statement.
In its statement, the Chinese defense ministry said aircraft must report a flight plan, "maintain two-way radio communications", and "respond in a timely and accurate manner" to identification inquiries.
The eight disputed islands, which are uninhabited, fall within China’s new aerial zone. China did not detail what measures it would take against aircraft that disobey its new orders, but defense experts say its military could scramble jets or even shoot down planes it views as a threat.
Responding to questions about the zone on an official state website, a defense ministry spokesman, Yang Yujun, said China set up the area "with the aim of safeguarding state sovereignty, territorial land and air security, and maintaining flight order".
"It is not directed against any specific country or target," he said, adding that China "has always respected the freedom of over-flight in accordance with international law".
"Normal flights by international airliners in the East China Sea air-defense identification zone will not be affected in any way."
The islands have been a source of tension between China and Japan for decades. In 2012, the Japanese government bought three of the islands from their Japanese owner, in a move that led to mass protests in Chinese cities.
Since then, Chinese ships have repeatedly sailed in and out of what Japan says are its territorial waters.
Taiwan, which also claims the islands, expressed "regret" at the move and promised that its military would take measures to protect national security.