Chinese authorities are once again giving warnings to the US navy after a U.S. destroyer sailed near Xisha islands in the South China Sea on Friday.

The Chinese defense ministry says the move was both illegal and provocative.

The ministry also says the act is clear evidence that the US is the real trouble-maker in the South China Sea, at a time when the overall situation in the region is embracing positive development.

The ministry warns that Chinese military will strengthen its surveillance and defense power in the region if needed, in a move to firmly protect China's national interests.

In the meantime, the Chinese foreign ministry describes the move as irresponsible and an act of provocation.

The foreign ministry urges the US navy to stop actions which go against China's sovereignty and maritime interests.

The guided-missile destroyer USS Decatur sailed within Chinese territorial waters on Friday.

The crossing drew a warning from Chinese warships to leave the area.

According to Chinese law, foreign warships need to gain approval from the Chinese government prior to entering Chinese waters.