Photos: New satellite imagery of Chinese island-building

China denounced what it called a “dangerous and provocative” act Tuesday after an American warship sailed within 12 nautical miles of a Chinese-built artificial island at the center of a regional dispute over maritime territory and sea routes.

The incident reflects rising tensions between the United States and China over Beijing’s aggressive program of land reclamation and construction on rocks and reefs in the Spratly archipelago in the South China Sea, whose shores include Vietnam, Taiwan and the Philippines.

The U.S. naval action was intended to uphold the principle of freedom of navigation in international waters, American officials said, and underscores that Washington does not accept China’s claim to territorial waters around the man-made islands.

Analysts said it also was aimed at reassuring nervous American allies that Washington will not allow Beijing to throw its weight around in the region unchallenged. But there is a risk it could have military consequences.

China said it viewed the move as an infringement on its sovereignty and claimed it would damage regional peace and stability.

The Foreign Ministry warned that Beijing might respond by speeding up its construction program. More ominously, the Chinese navy said further U.S. missions of this sort could “trigger eventualities” but did not elaborate.

China said it had followed the USS Lassen as it passed close to Subi Reef, sending out a missile destroyer and a patrol boat.

But a U.S. defense official said the mission had been completed “without incident.” The Lassen, a guided-missile destroyer, was accompanied by Navy surveillance planes, the official said, speaking on the condition of anonymity to discuss details of a sensitive military operation.

The decision to send the U.S. ship followed months of debate in Washington over how to find a balance between standing up to China and provoking a spiral of confrontation and regional militarization.

Last month, Beijing warned that it would “never allow any country” to violate what it considers its territorial waters and airspace around the islands.

Foreign Ministry spokesman Lu Kang said the U.S. vessel entered Chinese waters “illegally,” adding that Chinese authorities had tracked it and warned it as it passed.

“The action by the U.S. warship has threatened China’s sovereignty and security interests, endangered the safety of personnel and facilities on the islands and damaged regional peace and stability,” he said, urging the United States not to take further “dangerous and provocative actions.”

Referring to the United States, the spokesman said at a news conference, “If certain parties continue to stir up trouble and create tension, then China may be forced to come to the conclusion that it is indeed necessary for us to speed up and strengthen relevant capacity building” on the islands.

Hours later, China’s vice foreign minister, Zhang Yesui, summoned U.S. Ambassador Max Baucus to deliver a protest.

China claims almost all of the South China Sea as its territory, including the main islands and reefs. The Philippines, Vietnam, Malaysia, Brunei and Taiwan also have overlapping claims, and several of them occupy different islands, reefs and rocks.

China has carried out a massive program of land reclamation and construction on several islands since 2014, upsetting ties with the United States and several of those rival claimants.

This week’s naval mission is partly intended to test a pledge made by President Xi Jinping during his visit to Washington last month that Beijing would not militarize the islands.

Subi Reef, which lies close to the Philippines, used to be submerged at high tide before China began a dredging project to turn it into an island. It is now big enough to potentially host an airstrip.

Satellite images show what looks like a surveillance tower and multiple satellite antennas on Subi Reef, according to the Asia Maritime Transparency Initiative, part of the Center for Strategic and International Studies (CSIS).

Under the international law of the sea, turning such reefs into artificial islands does not imply any rights to territorial waters around them — although countries can claim a “safety zone” of 500 meters, or about 1,500 feet, around previously submerged reefs.

A Chinese airstrip is under construction at Fiery Cross Reef, and experts say another could soon be built at Mischief Reef. China says the construction work is primarily designed for civilian use and will not affect freedom of navigation in the South China Sea. Four other countries already have airstrips in the Spratlys.

Bonnie Glaser, an expert on the Chinese military at CSIS, said there were good reasons for the U.S. move.

“Some parts of the administration believed this would make things even more difficult, that China would become even more obstreperous, more difficult to deal with,” she said, “and others thought this wasn’t something we should do before Xi Jinping came to Washington.”

But in Beijing, retired Rear Adm. Yang Yi, a researcher at the Institute of National Strategic Studies at People’s Liberation Army National Defense University, said it would damage U.S-China relations and encourage China to speed up construction on the islands, and possibly militarize them.

“The act is reckless, dangerous and irresponsible,” he said. “It shows the United States has the mentality of the big brother but the temper of a child. If it becomes a regular thing, military conflict in the region is inevitable and the U.S. would be the one who started it.”

At September’s summit, President Obama told Xi that the United States would fly or sail anywhere that international law allows.

Additional patrols will follow in coming weeks and also could be conducted around islands that have been built up by Vietnam and the Philippines in the Spratlys, a U.S. defense official told the Reuters news agency.

“This is something that will be a regular occurrence, not a one-off event,” said the official, also speaking on the condition of anonymity. “It’s not something that’s unique to China.”

Yanmei Xie, senior China researcher with the International Crisis Group in Beijing, said that there was a risk of miscalculation and accidental clashes in such actions but added that doing nothing also would have consequences.

“Inaction would amount to acquiescing to the practice of taking unilateral actions to change the status quo in disregard of the international law of the sea,” she said. “It would undermine the credibility of the U.S. as an underwriter of regional security. It would sow doubt among American allies and friends about the U.S. commitment and the durability of its presence in the region.”

Xu Yangjingjing in Beijing and Craig Whitlock and Steven Mufson in Washington contributed to this report.

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