Japan warned of the danger of "unpredictable events" and South Korea voiced regret following China's unilateral declaration of an air defence zone over areas claimed by Tokyo and Seoul.
Japanese Foreign Minister Fumio Kishida said yesterday that his country was considering making stronger protests "at a higher level" after China announced it was setting up the zone over an area that includes Tokyo-controlled islands claimed by Beijing.
US Secretary of State John Kerry and Defence Secretary Chuck Hagel said yesterday they were "deeply concerned" at China's move and were committed to defending Japan.
China said it was setting up the "air defence identification zone" over an area including the islands in the East China Sea to guard against "potential air threats".
It released a set of aircraft identification rules that must be followed by planes entering the area.
Kishida told reporters that Japan cannot accept the Chinese measure, calling it "a one-sided action which leads us to assume the danger of unpredictable events on the spot", in remarks that later drew a rebuke from Beijing.
China said it "firmly" opposed Japan's remarks, with Foreign Ministry spokesman Qin Gang calling them "groundless and utterly wrong", according to the official Xinhua news agency.
Qin, who also urged the United States not to take sides over the issue, said Beijing had "lodged representation" with US ambassador Gary Locke over the American response to the air zone, calling for Washington to correct its mistakes.
Qin said the aims of the zone, which he asserted complies with international law, "are to protect China's state sovereignty and territorial and airspace safety". He added that the move did not target any specific nation "and will not affect the freedom of over-flights in relevant airspace."
The dispute over the islands, known as the Senkakus in Japan and the Diaoyus in China, heated up last year when Japan's government bought some of them from a private owner.
China has since sent coastguard vessels and other state-owned ships as well as aircraft close to the islands, sometimes breaching asserted airspace and territorial waters around them.
