Beijing says US warship near South China Sea island "provocation"

China denounced a US warship sailing close to a disputed island in the South China Sea occupied by Beijing as a "serious political and military provocation," a move that could further strain relations between the superpowers.

Beijing dispatched military vessels and fighter planes in response to warn off the US vessel, Foreign Ministry spokesman Lu Kang said in a statement late Sunday night, state news agency Xinhua reported.

The USS Stethem destroyer passed less than 12 nautical miles (22 kilometres) from tiny Triton Island in the Paracel Islands archipelago, which is also claimed by Taiwan and Vietnam, a US Defense Department official said.

The operation, meant to demonstrate freedom of navigation in disputed waters, came just hours before a previously scheduled phone call between President Donald Trump and his Chinese counterpart Xi Jinping.

"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 Chinese spokesman said, adding that Beijing would continue to take all necessary means to defend national sovereignty and security, according to Xinhua.

It was the second "freedom-of-navigation operation," or fonop conducted during the presidency of Donald Trump, following a drill in late May in which a US warship sailed within 12 nautical miles of an artificial island built up by China in the South China Sea.

Twelve nautical miles marks the territorial limits recognised internationally. Sailing within those 12 miles is meant to show that the United States does not recognise territorial claims there.

"Unlike in the Spratlys, where China has created new artificial territory in the last several years, it has effectively controlled the Paracels since 1974," said Mira Rapp-Hooper, a South China Sea expert at the Center for a New American Security. "It claims illegal straight baselines around the Paracels, and the fonop may have been contesting these."

Trump has heaped praise on Chinese President Xi Jinping, but his administration has also stepped up pressure on Beijing as he has become frustrated that China has not done more to pressure North Korea over its nuclear and missile programmes.