China is facing a test of diplomacy and power after a rash of border disputes in the South China Sea, experts say.
Neighboring countries have grown wary of China's military buildup following confrontations with Vietnam and the Philippines in offshore waters over the past month.
According to Vietnam, Chinese boats have repeatedly interfered with oil exploration surveys in Vietnam's exclusive economic zone since May 26.
The Philippines has also charged Chinese vessels with "serious violations" of sovereignty, citing a series of incidents in contested waters since February.
Both countries have staged naval maneuvers in a show of strength against China's presence and growing power in areas that it claims, hundreds of kilometers from its southern coast.
On June 14, Foreign Ministry spokesman Hong Lei pledged that China "will not resort to force or the threat of force" to resolve the disputes. But China has also warned Vietnam to stop "all invasive activities."
"Of course, they are a superpower," said Philippine President Benigno Aquino III, according to AFP News. "They have more than 10 times our population. We do not want any hostilities to break out."
Force
Analysts say countries in the region are reacting both to China's overlapping claims and its military expansion, despite the assurances that it will not use force.
"The one thing they have to do, certainly, is to sit down and really negotiate in good faith with these countries," said Elizabeth Economy, Asia studies director at the Council on Foreign Relations in New York.
Economy also urged China to stop sending its fishing, survey and patrol boats deep into the disputed areas, which are potentially rich sources of oil and gas.
"China seems to be provoking these other nations, despite its rhetoric to the contrary," she said. "What China has to do, simply, is give support to its words by its actual actions."
Instead, Beijing seems to be pressing its case with an ambiguous show of force by sending a 3,000-ton patrol ship on a two-week mission through the South China Sea to visit Singapore. The Haixun 31 set sail from the southern port of Zhuhai in Guangdong province on June 15, the official Xinhua news agency reported.
China will also double the fleet size of the State Oceanic Administration's maritime surveillance force to over 520 vessels by 2020, the official English-language China Daily said on June 17.
On the same day, Manila announced that its biggest warship, the destroyer escort BRP Rajah Humabon, would patrol disputed waters around Scarborough Shoal to check "security threats in the area," the Philippine Star reported.
On Monday, Singapore issued a statement urging China to "clarify its claims in the South China Sea with more precision as the current ambiguity as to their extent has caused serious concern in the international maritime community."
Naval expansion
The recent naval expansion of the People's Liberation Army (PLA) has been a growing regional concern with new projects like China's first aircraft carrier, which is scheduled for launch this year.
In March, the National People's Congress (NPC) announced that China's military budget would rise 12.7 percent to 601 billion yuan ($92.7 billion), although the Pentagon estimated last year that China's military-related spending was nearly twice as high as its official figures suggest.
"The limited military strength of China is solely for safeguarding its national sovereignty and territorial integrity and would not pose a threat to any country," an NPC spokesman said.
The policy formula leaves a large exception for defending the disputed maritime areas that China claims under its sovereignty, despite promises not to use force.
At times, China's statements on its buildup have appeared tailored to suit the occasion.
During the recent Shangri-La Dialogue security conference in Singapore, China's defense minister, Gen. Liang Guanglie, repeated assurances on military expansion.
"We do not intend to threaten any country with the modernization of our military force," said Liang, as cited by Reuters.
But in a fiery interview with state media last December, Liang voiced a very different view.
"In the coming five years, our military will push forward preparations for military conflict in every strategic direction," he was quoted as saying. "We may be living in peaceful times, but we can never forget war, never send the horses south or put the bayonets and guns away."
Energy resources
The mixed messages may be hard for China's neighbors to sort out as they deal with its far-flung claims to waters and energy resources offshore.
Bonnie Glaser, senior fellow at the Center for Strategic and International Studies in Washington, said the latest confrontation with Vietnam has been over oil surveys in an area that the country believed to be an undisputed part of its continental shelf.
Yet, China has reacted to the exploration as unilateral action in what it now calls disputed waters subject to its sovereignty and control.
"They claim that they are reacting, that they are being defensive, but the other countries of the region certainly don't see it that way," Glaser said.
The controversy may blur the line between offensive and defensive measures as countries like Vietnam conduct surveys that may lead to drilling for oil and gas.
"The Chinese are increasingly willing to disrupt other countries' abilities to engage in that exploration," said Glaser.
Uncertainties over maritime borders, sovereignty claims and military purpose have been compounded by shifts in China's interpretations.
"The positions of China are changing over time," Glaser said. "They're more fluid, they seem to be more sensitive about territorial integrity and sovereignty issues, and they seem to be less willing to tolerate any country exploiting the natural resources of the region."
Glaser believes China will be cautious about keeping its responses below a threat level that would solidify international opposition.
"The Chinese know that if they use their military capabilities against other countries that the entire region will then become so alarmed about China that they will lean very heavily on the United States," she said.
David Bachman, international studies professor at University of Washington in Seattle, said that regional economic growth and high oil prices have helped to intensify exploration in waters that have yielded few resources so far.
But over time, the signals from China have changed from the "peaceful rise" and reassurance policies of the mid- 1990s, he said.
"Something happened in 2009, and the leadership seems to have moved in more assertive directions, which are now drawing a reaction," said Bachman. "Certainly, Southeast Asia and others have not been reassured, and I don't think we're going back to that earlier status quo."
Resolution needed
China, Vietnam and the Philippines have agreed in the past on the principle of joint development of disputed areas, but they disagree on the maps of the areas in dispute.
Bachman said that some resolution is needed to bring the principle of joint development back into operation.
"If we're looking for a peaceful way to walk this back, proposals for joint peaceful development should be the appropriate measure, although whether nationalists in Vietnam, China and elsewhere are prepared to do that is in an open question," he said.