c China stepped up its criticism of the United States on Friday after a senior U.S. official said Washington had told Beijing it would not recognise an air defence zone over the disputed South China Sea if China set one up.
U.S. officials have expressed concern that an international court ruling expected in coming weeks on a case brought by the Philippines against China over its South China Sea claims could prompt China to declare an air defence identification zone, or ADIZ, as it did over the East China Sea in 2013.
U.S. Deputy Secretary of Defense Robert Work said on Wednesday the U.S. would view such a move as "destabilising" and would not recognise such an exclusion zone in the South China Sea, just as it did not recognise the one China established over the East China Sea.
Speaking a day after China's Defence Ministry accused Washington of "gesticulating" over the issue, Foreign Ministry spokesman Hong Lei said setting up an ADIZ had nothing to do with territorial disputes.
Whether to do set one up depended on whether China's air safety was being threatened and the level of the threat as well as other reasons, Hong told a daily news briefing.
"At present, as I've said, the situation in the South China Sea generally speaking is stable," he said.
China claims most of the South China Sea through which more than $5 trillion in ship-borne trade passes every year. Neighbours Brunei, Malaysia, the Philippines, Taiwan and Vietnam also have claims.
Hong also criticised Work for saying China's ADIZs had no basis in international law.
"The first person to set up an ADIZ was not China, but the United States," Hong said. "We can ask: what is the basis in international law for the U.S. setting up an ADIZ?"
The United States set up an ADIZ in 1950, at the start of the Cold War.
China drew condemnation from Japan and the United States when it imposed its ADIZ, in which aircraft are supposed to identify themselves to Chinese authorities, above the East China Sea.
China's comments come as President Xi Jinping told U.S. President Barack Obama that China would not accept violations of its sovereignty in the name of freedom of navigation - a reference to air and naval patrols the United States has conducted within what China considers its territorial waters.
Tensions between China and its neighbours over sovereignty in the South China Sea have risen after Beijing embarked on significant land reclamation on disputed islands and reefs in the area.
This week Malaysia said it had summoned the Chinese ambassador over what Kuala Lumpur said was an encroachment by a large number of Chinese-flagged boats in the South China Sea.
Hong said both countries had a "different understanding" of the situation, but added China would handle it via bilateral channels.