SINGAPORE — The United States has spotted a pair of mobile artillery vehicles on an artificial island that China is building in the South China Sea, a resource-rich stretch of ocean crossed by vital shipping lanes, US officials said.
China’s construction program on previously uninhabited atolls and reefs in the Spratly Islands has already raised alarm and drawn protests from other countries in the region, whose claims to parts of the South China Sea overlap China’s.
Defense Secretary Ashton B. Carter called this week for China to halt the construction, saying international law did not recognize Chinese claims of sovereignty over the new territories and saying US warships and military aircraft would continue to operate in the area.
The artillery was spotted by satellites and surveillance aircraft about a month ago, and the two vehicles have since been either hidden or removed, according to US officials who spoke about intelligence matters on the condition of anonymity.
“It is unclear whether they have been removed,” one of the officials said.
Another said that even if the weapons are still on the island, they pose no threat to US naval forces or aircraft in the region, although the guns could reach some nearby islands claimed by other countries.
With Carter in Singapore to attend the Shangri-La Dialogue, a high-profile annual Asian security meeting that Chinese officials also are attending, US officials were reluctant to publicly discuss the intelligence they had collected about the artillery.
Brent Colburn, a spokesman traveling with Carter, would say only that the United States was aware of the weapons.
Senator John McCain, an Arizona Republican who heads the Senate Armed Services Committee, criticized China’s deployment of artillery on the island as “a disturbing development and escalatory development.”
“Their actions are in violation of international law, and their actions are going to be condemned by everyone in the world,” McCain was quoted by Reuters as saying in Ho Chi Minh City, where he stopped Friday on his way to Singapore for the security conference.
“We are not going to have a conflict with China,” he said, “but we can take certain measures, which will be a disincentive to China to continue these kinds of activities.”
There was no immediate comment from Chinese officials about the weapons.
A top Chinese military official, Admiral Sun Jianguo, is scheduled to speak at the conference in Singapore about Chinese military policies. Sun, the deputy chief of staff of the People’s Liberation Army, which includes the navy, will lead the strongest delegation of military officials that China has yet sent to the annual forum.
China released a military strategy document this week that, for the first time, called for its navy to project force beyond its coastal waters into the open oceans. Western officials said the document, because of its timing, seemed intended as a challenge to other participants in the conference.
The heightened tensions between the United States and China over the South China Sea were on display last week when the United States sent a surveillance plane close to Fiery Cross Reef, which China has built into an island with a runway that military aircraft can use. The Chinese told the US plane to leave the area, according to a CNN crew aboard the flight.
When a US littoral combat ship, the Fort Worth, conducted a weeklong patrol of waters near the Spratly Islands, including Fiery Cross Reef, a Chinese guided missile frigate followed the US vessel for a time, the Pentagon said. Other US warships will do similar patrols, which will be the “new normal” for the Navy in the South China Sea, the Pentagon said.
China has said it was building the islands in the sea largely for civilian purposes, but it has not denied that it also envisions a military role for them.