The United States warned China on Friday against any move to declare a new air defense zone over parts of the South China Sea including disputed islands.

The Asahi Shimbun daily of Japan reported that Chinese air force officials have drafted proposals for the next Air Defense Identification Zone (ADIZ) that could place the Paracel Islands at its core.

Any such move would be seen "as a provocative and unilateral act that would raise tensions and call into serious question China's commitment to diplomatically managing territorial disputes," State Department deputy spokeswoman Marie Harf told reporters.

She stressed, however, that the reports were "unconfirmed” at this time.

Beijing claims the South China Sea almost in its entirety, even areas a long way from its shoreline.

Late last year, it caused a storm when it abruptly declared an ADIZ above the East China Sea, including islands at the heart of a sovereignty row with Tokyo.

"We've made very clear that parties must refrain from announcing an ADIZ or any other administrative regulation restraining activity of others in disputed territories, and we would of course urge China not to do so," Harf added.