U.S. Secretary of State John Kerry says unannounced, unilateral actions in contested waters of the South China Sea challenge regional stability.
After meeting with leaders in Beijing to discuss rival maritime claims between China, the Philippines, Vietnam, and Malaysia, Kerry then traveled to Indonesia on Saturday, where officials are working with the Association of South East Asian Nations, or ASEAN, to help resolve those disputes.
Stepped-up Chinese patrols in the South China Sea raise fears among rival territorial claimants that Beijing may move to create the same kind of air defense zone there as it now has around islands claimed by Japan in the East China Sea.
Kerry told Chinese President Xi Jinping that Washington is hoping for better transparency in the South China Sea to reduce possible "misinterpretations." Assistant U.S. Secretary for East Asian Affairs Danny Russel says China is engaged in an "incremental pattern of assertiveness."
"No one can justifiably, in compliance with international law, simply assert the right to exercise control over great swaths of a sea," he said.
Beijing agrees the disputes should be settled through international law but says Washington should be careful not to make things worse.
"The United States is not a direct party in the South China Sea dispute and should keep its commitment of not taking sides on issues of territorial sovereignty and be cautious in words and actions," said Hua Chunying, spokeswoman for China's foreign ministry.
Much of the concern over the South China Sea is based on commercial shipping there. Beijing University analyst Jia Qingguo contends that shipping will not be affected by China's so-called nine-dash line, a U-shaped line on maps marking its claim of sovereignty over a wide area including the disputed Spratley and Paracel Islands.
"The Chinese government has repeatedly stated that there is freedom of navigation within the nine-dash line," said Jia. "In other words, the nine-dash line is not in [conflict] with the U.S. request of freedom of navigation."
American University professor Lou Goodman says pressures of trade and security make the South China Sea a potentially dangerous flashpoint for Beijing and Washington.
"A power like China, a power like the United States can't back off of anything," he said. "New solutions have to be found to disputes like this that are win-win for the sides that are talking."
The United States is pushing to settle rival claims through the regional ASEAN alliance.
"These are all countries that it would be well worth China developing stronger harmonious relations with," Goodman added. "And having conversations like this might be a good step forward in general in addition to focusing on the particular dispute that they are talking about."
But smaller ASEAN countries fear being bullied by China, and Washington's reliance on Beijing on issues such as Syria and Iran offer them little reassurance, says American Enterprise Institute analyst Michael Auslin.
"The U.S. has so little influence over China, or has chosen to act toward China in ways that minimize any influence it really could have," he said. "Obviously China looks at ASEAN as at best a negotiating partner, at worst [as] a collection of countries they can pick apart at their time of choosing."
Indonesia is an important stop for Kerry's efforts on the South China Sea as it is home to the ASEAN secretariat and a government that is playing an increasingly important role in resolving the rival maritime claims as a leading economy that has good relations with Beijing.