BEIJING: The United States defied China Tuesday by sending a warship close to artificial islands the rising Asian power is building in disputed waters, prompting Beijing to summon the US ambassador and denounce what it called a threat to its sovereignty.

The USS Lassen passed within 12 nautical miles — the normal limit of territorial waters around natural land — of at least one of the formations Beijing claims in the South China Sea.

China’s defense ministry said a destroyer-class ship and another frigate were dispatched to “warn” the US vessel, which Beijing said it had “shadowed.”

Washington’s long-awaited move appeared to escalate tensions over the strategically vital waters, where Beijing has rapidly transformed reefs and outcrops into artificial islands with potential military use.

China claims sovereignty over almost the whole of the South China Sea, raising concerns it could one day dictate who may transit its busy sea lanes.

Several neighboring countries including the Philippines, a US ally, have competing claims and the dispute has raised fears of clashes in an area through which a third of the world’s oil passes.

The US action was part of its “routine operations in the Sea in accordance with international law,” an American official told AFP. “We will fly, sail, and operate anywhere in the world that international law allows.”

China’s deputy foreign minister Zhang Yesui summoned US Ambassador Max Baucus on Tuesday to announce that the USS Lassen had engaged in a “serious provocation,” the official news agency Xinhua said.

“The Chinese government will resolutely safeguard territorial sovereignty and legal sea interests, and China will do whatever necessary to oppose deliberate provocation from any country,” Zhang added.

A foreign ministry spokesman said that the ship had “illegally entered” waters near the islands.

Fiery state-run tabloid the Global Times hinted in an editorial that Beijing could respond more strongly if the US made similar trips in the future. “We should first track the US warships. If they, instead of passing by, stop for further actions, it is necessary for us to launch electronic interventions, and even send out warships, lock them by fire-control radar and fly over the US vessels,” it said.