The United States warned China on Wednesday against taking "additional provocative actions" following an impending international court ruling on the South China Sea that is expected to largely reject Beijing's broad territorial claims.
A senior State Department official voiced skepticism at China's claim that dozens of countries backed its position in a case the Philippines has brought against Beijing and vowed that Washington would uphold U.S. defense commitments.
Colin Willett, deputy assistant secretary of state for East Asia, said Washington had "a lot of options" to respond to any such Chinese moves in a region she said was vital to U.S. interests. She also made clear that with a ruling expected possibly within weeks, the United States was working to rally sometimes wavering allies and partners in the region to ensure a unified front.
How Washington handles the aftermath of the ruling is widely seen as a test of U.S. credibility in a region where it has been the dominant security presence since World War Two but is now struggling to contain an increasingly assertive China.
"We, the United States, do have very clear national interests in the area," Willett told Reuters.
"We have an interest in upholding our defense commitments and our security partnerships."
The Philippines is contesting China's claim to an area shown on its maps as a nine-dash line stretching deep into the maritime heart of Southeast Asia, covering hundreds of disputed islands and reefs and encompassing a vital global trade route.
The consensus among officials and analysts inside and out the region is that the ruling will go largely against Beijing.
U.S. officials have warned China against declaring an air defense identification zone in the South China Sea, as it did in the East China Sea in 2013, and against stepping up its building and fortification of artificial islands.
They say that beyond diplomatic pressure, the U.S. response to such moves could include accelerated "freedom-of-navigation" patrols by U.S. warships and overflights by U.S. aircraft as well as increased defense aid to Southeast Asian countries.
Willett said that while it was still unclear how the Permanent Court of Arbitration in The Hague would rule, "it isn't in (China's) interest to take additional provocative actions" after it does.
Willett reiterated the U.S. view that the ruling must be binding. She declined to detail how the United States might respond should Beijing stick to its vow to ignore the ruling, but said: "I do think it’s an important inflexion point, not just for the United States, but for the whole region."
Willett said Washington hoped China would see the ruling as "an opportunity to restart serious discussions with their neighbors."
China has accused the United States of "hyping" the issue and warned in May that international complaints about its actions in the South China Sea would snap back on its critics. But it has largely avoided specific threats of how it might respond to the arbitration ruling.
On Monday, U.S. Navy chief Admiral John Richardson said China's large-scale land reclamation in the South China Sea and militarization of artificial islands had extended its potential ability to deny access to some of the world's busiest shipping lanes.
The U.S. aircraft carriers John C. Stennis and Ronald Reagan staged joint operations last weekend in seas east of the Philippines in a show of strength ahead of The Hague ruling, prompting strong Chinese criticism.
China has listed more than 40 countries it says supports its position on the arbitration case. Willett said it was not even clear what those countries "have allegedly agreed to."
"There's some skepticism about that grouping," she said.
Only eight countries have publicly supported China's position, including land-locked states such as Niger and Afghanistan, according to Washington's Center for Strategic and International Studies.
Willett played down an apparent display of disunity by Southeast Asian countries last week. The Association of Southeast Asian Nations (ASEAN), following a foreign ministers meeting in China, issued and then abruptly withdrew a statement that expressed deep concerns over tensions in the South China Sea, a retraction widely seen as the result of Chinese pressure.
A senior U.S. official said ASEAN countries were "under an intense amount of pressure" and made clear that behind the scenes, Washington was working to stiffen their resolve.