China warns US 'not to make trouble' in South China Sea

China has warned the United States to "think twice" before sending a warship into the South China Sea to challenge its claims in the area.

State news agency Xinhua reported Tuesday that Chinese Foreign Minister Wang Yi had advised the U.S. "not to make trouble out of nothing" over the issue.

China has constructed two artificial islands — Subi and Mischief reefs — in the Spratly chain, an area to which Vietnam, Brunei, Malaysia, Taiwan, and the Philippines have also laid claims.

Wang's remarks came during a seminar in Beijing, after he was asked to comment after reports that a U.S. warship had sailed within 12 nautical miles (22 kilometers) -- the extent of territorial waters -- of the islands.

"We are checking out the matter," said the foreign minister. "If it is true, we advise the U.S. to think twice before its action."

In October, the U.S. Navy was reported to be preparing to conduct "freedom of navigation" operations in the waters.

Last month, U.S. Secretary of Defense Ash Carter said his country "will fly, sail and operate wherever the international law allows, as we do around the world".

At an Oct. 8 briefing, White House Spokesman Josh Earnest said warships that patrol close to the islands "should not provoke significant reaction from the Chinese".

The United States and Japan have expressed alarm at China's expansion, which they suspect is aimed at extending its military reach, while the Philippines -- which calls the area the West Philippine Sea -- has taken the quarrel to the International Tribunal for the Law of the Sea in The Hague.

Last year, China began a massive reclamation project on about half a dozen land features in the area, adding about 3,000 acres (1200 hectares) of artificial land and turning what were mere rocks barely above water at low tide into artificial islands large enough to host runways capable of accommodating high-performance jet aircraft and naval docking.