BEIJING -- The intensifying disputes between China and four of its Southeast Asian neighbors over claims in the South China Sea have begun to raise warnings over the prospect of open conflict.
The disputes, enmeshed in the competition for energy resources, have reached an impasse, according to a new report by the International Crisis Group, a nongovernmental research organization that has become a leading authority on the frictions.
"All of the trends are in the wrong direction, and prospects of resolution are diminishing," said the report, titled "Stirring Up the South China Sea: Regional Responses."
The pessimistic conclusion came a day after China stepped up its political and military control of Nansha and Xisha islands, which both Vietnam and the Philippines claim, and Zhongsha, claimed by the Philippines.
On Monday, the Philippine president, Benigno S. Aquino III, announced plans to buy new aircraft and attack helicopters that could be used in territorial disputes in the South China Sea. China and the Philippines have competing claims there over the Scarborough Shoal and potentially energy-rich underwater ground around Reed Bank, among other areas.
In a speech before a joint session of the Philippine Congress, Mr. Aquino adopted an aggressive stance against an unspecified threat. "If someone enters your yard and told you he owns it, will you allow that?" he said. "It's not right to give away what is rightfully ours."
The Chinese Foreign Ministry responded on Tuesday, saying that the Philippine president had no legal standing to rely on the United Nations Convention on the Law of the Sea as the basis for its claim on Huangyuan Island, the Chinese name for the Scarborough Shoal.
The analysis by the International Crisis Group apportions blame to both China and its neighbors for the ratcheting up of incidents and tensions in the sea, one of the most traveled waterways in the world, and a vital strategic pathway for the United States and its allies in the Asia-Pacific region. The group's Beijing office, led by Stephanie Kleine-Ahlbrandt, has spent two years studying the South China Sea, interviewing decision makers in China and the claimant countries. It released an earlier report in the same overall regional study in April, focused on the internal military and civilian agencies that play a role in China's actions in the South China Sea, ranging from the People's Liberation Army to a fisheries bureau.
The vagueness of China's claims to islands and energy resources in the sea has "rattled" other claimants, the new report said. China bases some of its claims in the sea on discoveries by ancient Chinese navigators. More specifically, China lays claim to everything within a so-called nine-dash map drawn shortly after World War II. By some estimates, the nine dashes incorporate 80 percent of the South China Sea.
But China's assertive approach has been matched by Vietnam and the Philippines, two countries that are more forcefully defending their claims and enlisting outside allies, the report said.
"South China Sea claimants are all anxious to pursue oil and gas exploration in the portions of the sea that they claim, and are concerned with protecting their claimed fishing grounds as coastal waters become depleted," it said. The fact that the waters are mostly patrolled by civilian vessels run by national governments was little comfort.
"In spite of being more lightly armed and less threatening than navy ships, civilian law enforcement vessels are easier to deploy, operate under looser chains of command and engage more readily in skirmishes," it said.
In an example of civilian vessels plying the South China Sea with possibly serious consequences, the Philippine Foreign Ministry said Tuesday that it objected to a fleet of 29 fishing vessels, a cargo vessel and three other ships, protected by a Chinese Navy vessel near Fiery Cross Reef and Subi Reef, two areas of the South China Sea that the Philippines claims.
Bree Feng contributed research.
This article originally appeared in The New York Times.