The US Defence Department said it would "welcome" future air patrols by Japan over the South China Sea, where China is involved in territorial disputes with some countries. But the US State Department appeared not to be in step with the Pentagon over Japan's possible involvement in such an operation.

The two departments were commenting on a recent report that Admiral Robert Thomas, top commander of the US Navy's 7th Fleet, favoured air patrols by Japan over the waters.

Jen Psaki, a State Department spokeswoman, said the United States welcomed "a more active role for Japan in ensuring stability and security in Asia. But we're not aware of plans or proposals for new patrols."

Chinese Foreign Ministry spokeswoman Hua Chunying said on Friday that countries outside the region should "refrain from sowing discord among other countries".