A U.S. navy warship sailed close to a disputed reef in the South China Sea on Tuesday, a U.S. Department of Defense official said, days after China warned criticism of its claims in the crucial waterway would rebound like a coiled spring.
The freedom of navigation operation by the USS William P. Lawrence, travelling within 12 nautical miles of Chinese-occupied Fiery Cross Reef, was to "challenge excessive maritime claims of some claimants in the South China Sea", Defense Department spokesman Bill Urban said.
"These excessive maritime claims are inconsistent with international law as reflected in the Law of the Sea Convention in that they purport to restrict the navigation rights that the United States and all states are entitled to exercise," Urban said in an emailed statement.
Facilities on Fiery Cross Reef include a 3,000-metre (10,000-foot) runway and Washington is concerned China will use it to press its extensive territorial claims at the expense of weaker rivals.
U.S. naval officials also believe China has plans to start reclamation and construction activities on Scarborough Shoal, which sits further north of the Spratlys within the Philippines claimed 200 nautical mile (370 km) exclusive economic zone.
China claims most of the South China Sea, through which $5 trillion in ship-borne trade passes every year. The Philippines, Vietnam, Malaysia, Taiwan and Brunei also have overlapping claims.
The Pentagon last month called on China to reaffirm it has no plans to deploy military aircraft in the disputed Spratly Islands after Beijing used a military plane to evacuate sick workers from Fiery Cross.
"Fiery Cross is sensitive because it is presumed to be the future hub of Chinese military operations in the South China Sea, given its already extensive infrastructure, including its large and deep port and 3000-metre runway," said Ian Storey, a South China Sea expert at Singapore's ISEAS Yusof Ishak Institute.
"The timing is interesting, too. It is a show of U.S. determination ahead of President Obama's trip to Vietnam later this month," Storey added.
Speaking in Hanoi ahead of Obama's visit, Daniel Russel, the Assistant Secretary of State for East Asia and the Pacific, said freedom of navigation operations were important for smaller nations.
"If the world's most powerful navy cannot sail where international law permits, then what happens to the ships of navy of smaller countries?," Russel told reporters in Hanoi before news of the operation was made public.
"If our warships can't exercise its legitimate rights under international law at sea, then what about the fishermen, what about the cargo ships? How will they prevent themselves from being blocked by stronger nations?"
The move also comes as tough-talking city mayor Rodrigo Duterte looks set to take the Philippines' presidency. He has proposed multilateral talks on the South China Sea.
China has reacted with anger to previous U.S. freedom of navigation operations, and says that there has never been a problem with freedom of navigation or overflight in the South China Sea.
The U.S. flew fighter planes near the disputed Scarborough Shoal last month, drawing protests from China. Last November, two U.S. B-52 long-range bombers flew near to Chinese facilities under construction on Cuarteron Reef in the Spratlys.
Criticism of China over the South China Sea will rebound like a coiled spring, a Chinese diplomat said on Friday, as a U.S. warship visited Shanghai against a backdrop of rising tension in the region.