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 on 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 official told AFP news agency.

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

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"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.

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

The operation is the second of its kind carried out by the US since Trump took office.



The first was on May 25, when the USS Dewey, a guided-missile destroyer, sailed less than 12 nautical miles from Mischief Reef - part of the disputed Spratly Islands south of the Paracel Islands.

China claims nearly all of the South China Sea, despite partial counter-claims from Taiwan and several southeast Asian nations including the Philippines, Brunei, Malaysia and Vietnam.

China has rapidly built reefs into artificial islands capable of hosting military planes.

Freedom of navigation operations are designed to challenge the sovereignty of countries with claims to disputed territory. Washington has challenged annexations of South China Sea islets while advocating for a diplomatic settlement.

China has recently built up its facilities on Triton Island, including a new helicopter landing site, according to the Asia Maritime Transparency Initiative, part of the Center for Strategic and International Studies think-tank.

A large Chinese flag is displayed on the island, visible from aerial and satellite photos.

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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.

On Thursday, the administration imposed sanctions on two Chinese citizens and a shipping company for helping North Korea's nuclear and missile programmes and accused a Chinese bank of laundering money for Pyongyang.

The Trump administration has also approved an arms package for Taiwan worth about $1.4bn, the state department said last week. China deems Taiwan its own and has never renounced the use of force to bring the self-ruled island under its control.

Trump is due to speak to Chinese President Xi Jinping and Japanese Prime Minister Shinzo Abe on Sunday in advance of meetings he will hold with both leaders on the sidelines of the Group of 20 summit in Hamburg, Germany, next Friday and Saturday.