A new potential flashpoint has emerged in the standoff between China and the U.S. over disputed areas of the South China Sea amid concerns that Beijing is considering expanding the area where it is seeking to reclaim islands and extend its influence.
China has been expanding and developing islands in the Spratly Islands chain. But the U.S. military about a month ago observed Chinese ships conducting survey work around a clump of rocks, sandbars and coral reefs known as the Scarborough Shoal, far from the Spratlys. Scarborough Shoal is 120 nautical miles off the coast of the Philippines, a close U.S. ally, and just 200 nautical miles from its capital Manila. It is around 470 nautical miles from the closest point on the Chinese mainland.
Signaling its concern, the U.S. flew three different air patrols near Scarborough in recent days, including on April 19 and 21, according to U.S. defense officials. The first of the flights, in a message to Beijing that the shoal is central to maritime security in the region, came just four days after Defense Secretary Ash Carter announced a series of joint patrols with the Philippines. The U.S. Air Force disclosed the April 19 flights in a news release.
“Our job is to ensure air and sea domains remain open in accordance with international law. That is extremely important, international economics depends on it—free trade depends on our ability to move goods,” said Col. Larry Card, Commander of Pacific Air Force’s Air Contingent, which conducted the patrols. “There’s no nation right now whose economy does not depend on the well-being of the economy of other nations.”
Beijing on Monday condemned the U.S. flights, saying the shoal, which it calls Huangyan Island, is China’s “inherent territory.”
In recent weeks, the U.S. had sought to “lower the temperature” over Scarborough, a senior U.S. official said. According to other U.S. officials, that included canceling one “freedom of navigation” patrol in the South China Sea that had been planned for this month.
But last week’s U.S. air patrol has heightened tensions once again, and could lead to more Chinese activity in the area, according to Chinese security analysts.
China’s defense ministry responded on Monday with a statement on its website expressing “concern and opposition,” and accusing the U.S. of militarizing the South China Sea. “The Chinese military will take all necessary measures to safeguard national sovereignty and security,” it said.
There is no sign yet of any land reclamation at the Chinese-held atoll, which sits some 250 nautical miles northeast of the artificial islands Beijing has built in the disputed Spratlys archipelago over the past two years.
Even so, there is growing concern among U.S. and Philippine officials that Beijing plans to begin such work at the shoal, possibly in response to a ruling on its territorial claims by an arbitration panel in The Hague, expected this summer.
Any such work would come close to a red line for the U.S. and the Philippines, given the proximity to the country and to Philippine military bases where U.S. forces were redeployed this month.
Washington and its allies also would consider it a major escalation. Beijing seized control of the shoal from Manila in 2012, whereas the artificial islands in the Spratlys were built on rocks and reefs already controlled by China.
Last week, Mr. Carter, visiting the Philippines, announced a number of initiatives aimed to “modernize” the U.S.-Philippines alliance, including a rotating deployment of U.S. military aircraft at Clark Air Base in the Philippines.
The six U.S. aircraft that flew near Scarborough Shoal on April 19 are based at Clark. The four A-10 Thunderbolt fighters and two HH-60 Pave Hawk helicopters “conducted a flying mission through international airspace…providing air and maritime situational awareness,” the U.S. Air Force statement said.
The aircraft did not fly to within 12 nautical miles of Scarborough, according to a U.S. official, which would have amounted to a legal challenge to China’s claims on the shoal, but the proximity of the flights was clearly intended to send a message to Beijing.
The U.S. patrol came a month after the U.S. chief of naval operations, Adm. John Richardson, said that the U.S. military had observed Chinese ships doing survey work around the shoal that could be a prelude to reclamation. U.S. officials say the shoal has been largely quiet since, with the exception of a medical military flight that rescued three injured civilians, according to a U.S. official.
The U.S. has used its Navy and Air Force to challenge Chinese claims in the region, but has approached the dispute with caution, to avoid provoking a broader confrontation.
But, amid criticism over that approach from senior congressional and military figures, stronger action is likely if China made a move on Scarborough Shoal, U.S. officials said.
“We’re prepared to take steps that reinforce our long-standing position in the South China Sea,” a senior administration official said.
Steps could include economic sanctions, a buildup of military assets in the area, or taking a more overt position on the legal status of land features in the South China Sea.
Another option is to rescind China’s invitation to the U.S.-led Rim of the Pacific, or Rimpac, joint naval drills in Hawaii in the summer. Disinviting China from the exercise, some U.S. officials and others believe, would amount to a public shaming that would resonate in Beijing.
Chinese security analysts said Beijing reserved the right to build on the shoal and considered it a valuable fishing ground, as well as legally important because it includes rocks that are potentially entitled to 12 nautical miles of territorial seas.
China is conscious, however, that any reclamation there would be provocative.
“Of course there’s no exclusion for some sort of move like lighthouse construction or a maritime monitoring post, but sizable land reclamation on Scarborough Shoal is out of the question,” said Zhu Feng, a security expert at Nanjing University.
Beijing may be using the shoal as a bargaining chip, rather than actively seeking to establish another military outpost there, some analysts said.
“They imply that they may want Scarborough Shoal, then they will back off and show that they are a good international player,” said Bryan Clark, a former senior adviser to the chief of naval operations who is now an adviser at the Center for Strategic and Budgetary Assessments, a think tank in Washington.
Any outpost at the shoal would be vulnerable to attack in a military conflict because of its remote location and proximity to the Philippines.
In peacetime, however, combined with the Spratlys and the Paracels, an archipelago to the north, even a small outpost would complete a triangle of military installations that could help China control waters and airspace in between.
It also could be used to help China to monitor and intercept patrols by the U.S. and its allies from bases in the Philippines, as well as to track ships and submarines entering the South China Sea from the Philippine Sea.
“It would allow China to monitor, patrol, and intervene anywhere in the South China Sea, with the ultimate goal of establishing de facto (if not legal) control over the sea,” said Gregory Poling, a maritime expert at the Center for Strategic and International Studies.
Write to Gordon Lubold at Gordon.Lubold@wsj.com and Jeremy Page at email@example.com