BEIJING -- China said on Sunday that the US missile destroyer trespassing China's territorial waters off the Xisha Islands was "serious political and military provocation."

Foreign Ministry spokesperson Lu Kang said in a statement released on Sunday night that China dispatched military vessels and fighter planes in response to warn off the US vessel.

Earlier Sunday, the missile destroyer USS Stethem trespassed China's territorial waters off the Xisha Islands.

The Xisha Islands are an inherent part of the Chinese territory, Lu said, noting that in accordance with the Law of the People's Republic of China on the Territorial Sea and the Contiguous Zone, the Chinese government promulgated the baseline of the territorial sea off the Xisha Islands in 1996.

"The relevant Chinese law has explicit provisions on foreign military vessels' entry into the territorial sea of China," Lu said.

Under the pretext of "navigation freedom," the US side once again sent a military vessel into China's territorial waters off the Xisha Islands without China's approval, Lu said, stressing that its behavior has violated the Chinese law and relevant international law, infringed upon China's sovereignty, disrupted peace, security and order of the relevant waters and put in jeopardy the facilities and personnel on the Chinese islands.

The behavior constitutes a serious political and military provocation, Lu said, stressing that the Chinese side is strongly dissatisfied with and firmly opposed it.

Working together, China and ASEAN member states have cooled down and improved the situation in the South China Sea, according to Lu, noting that the United States, who deliberately stirs up troubles in the South China Sea, is running in the opposite direction from countries in the region who aspire for stability, cooperation and development.

"The Chinese side strongly urges the US side to immediately stop such kind of provocative operations that violate China's sovereignty and threaten China's security," the spokesman stressed, saying the Chinese side will continue to take all necessary means to defend national sovereignty and security.