China's Defence Ministry said on Monday it had lodged formal protests with the U.S. and Japanese embassies in China after both countries criticised Beijing's plan to impose new rules on airspace over disputed waters in the East China Sea.
The ministry said the criticism was unfounded and irresponsible. It also called on the United States to stop taking sides in the row with Japan over a group of uninhabited disputed islands in the East China Sea.
China on Saturday published coordinates for a newly established "East China Sea Air Defense Identification Zone", which covers most of that sea and includes the skies over the disputed islands.
Beijing warned that it would take "defensive emergency measures" against aircraft that failed to identify themselves properly in the airspace, prompting both Washington and Tokyo to sharply criticise the move.
China said the new rules would not affect "normal operations" for international flights. Several Asian airlines contacted by Reuters said their flights would not be impacted.
China's Defence Ministry said it was within the country's right to set up the zone.
"Japan's remarks are unjustified - China will never accept them," spokesman Yang Yujun said in a statement on the ministry's website.
"We reiterate that the purpose of China's approach is to defend national sovereignty and territorial airspace security, maintain the order of airspace flight, and is an effective exercise of our right of self defence," Yang said.
U.S. Secretary of State John Kerry over the weekend urged China to exercise caution and restraint, saying freedom of overflight was essential to stability and security in the Pacific.
Yang said China's move complied with the U.N. charter and international law.
The United States should stop taking sides in the dispute, and stop making "irresponsible remarks" on the new airspace zone, Yang added.
"The United States, on the issue of the Diaoyu islands, must earnestly not take sides, not make inappropriate remarks and not give the wrong signal to Japan and encourage (its) risky behaviour," Yang said.
Sino-Japanese relations have been strained for months because of the dispute over the tiny islands in the East China Sea, known as the Senkaku in Japan and the Diaoyu in China.
A South Korean transport ministry official said South Korean planes flying in that airspace would notify China's civil aviation authorities of their flight plans.
An official at the Japan Civil Aviation Bureau said airlines had been advised to take greater care in the area, although the warning was general rather than related to anything specific.