A buoy, posts and building materials on an inhabited outcrop sound unremarkable, but they mark an escalation of a dispute over one of the world’s busiest shipping lanes, resource wealth, and how Southeast Asia manages China’s rise as a regional power.

Harsh rhetoric and an occasional stand-off have long been part of the jousting over the contested East Sea, but recently the incidents are more frequent and the complaints from Southeast Asian capitals about China’s actions are louder.

The region cannot take on Beijing militarily, but nor do they want to roll over and lose territories near their coastlines. Internationalizing the dispute, including encouraging a U.S. presence in the sea, is one way to protect their interests.

“I am increasingly favoring the word aggressive over assertive in describing China’s behavior in the South China Sea. And that is a fairly important distinction,” said Ian Storey, a fellow at the Institute of Southeast Asian Studies in Singapore.

In recent weeks China and Vietnam have traded accusations of violating each others sovereignty at sea. It is the Philippines’ claims that China erected poles, placed a buoy and left building materials near the Amy Douglas Bank that is most serious of recent incidents, amounting to an accusation that Beijing has breached the 2002 Declaration of the Code of Conduct of Parties in the South China Sea (DOC).

The DOC is a non-binding agreement between China and the Association of South East Asian Nations (ASEAN). It calls for restraint and avoiding activities that might escalate tensions, including the occupation of uninhabited land — a provision that Manila says has been “aggressively violated.”

China, which says Manila is violating its sovereignty, says the materials were for scientific purposes on its territory and there was no intention to occupy or seize the reef.

“Whether it is military or not… I think if there is new building on a previously unoccupied feature, that would be a fairly clear breach of the DOC,” said Euan Graham, senior fellow in the Military Studies Program at the S. Rajaratnam School of International Studies in Singapore.

The South China Sea covers more than 648,000 sq miles (1.7 million square km), including more than 200 mostly uninhabitable islands, rocks and reefs, the ownership of which confer rights to the surrounding waters — and the oil and gas they are thought to contain, as well as fishing rights.

Although there are six claimants to some or all of the sea — China, Taiwan, Vietnam, Philippines, Malaysia and Brunei — and many claims overlap, the dispute is often seen as China, which has the largest claim, against the rest.

The problem is how to determine ownership. The United Nations Convention on the Law of the Sea (UNCLOS) gives a country sovereignty over seas up to 12 nautical miles (22.2 km/13.8 miles) from its coast, including of islands.

There is also a 200 nautical mile Exclusive Economic Zone that gives jurisdiction over natural resources, scientific research and building structures. Recent incidents have been inside the EEZ’s of Vietnam and the Philippines.

China says its historical sovereignty dates back to the 7th century and supersedes any modern claims to the sea, but says it is ready to cooperate with others on joint exploration.

Even how to negotiate is an issue. China wants bilateral talks, but the Southeast Asian states favor going through the 10-member ASEAN, which also opens a door to a role for the United States.

“The South China Sea has caused most Southeast Asian states to press for the U.S. to remain engaged in Southeast Asia,” said Carlyle Thayer, a professor at the Australian Defense Force Academy.

The risk is that too great a U.S. role antagonizes China, which reacted angrily when the United States was among the parties to raise the issue at an ASEAN forum last year. “Southeast Asia wants U.S. support, but does not want the U.S. to complicate the issue or take actions that would isolate China and force them to takes sides,” Thayer said.

Another issue for ASEAN is that the dispute does not affect all 10 members, but mostly involves Vietnam and the Philippines, with Malaysia and Brunei also having claims.

Others, such as Thailand, Myanmar and Laos, have no claim and so have less incentive challenge Beijing on the issue, while China is an increasingly important trading partner for all countries in the region.

As the monsoon and typhoon season starts, Manila is worried about a repeat of Mischief Reef, 135 nautical miles west of the southwestern island of Palawan.

In February 1995, the Philippines found a Chinese structure on the reef, which it said was a military installation but Beijing said was a shelter for fisherman. The structure had been built when the Philippine navy was unable to patrol due to the bad weather.

The Amy Douglas Bank is about 125 nautical miles off Palawan. The Philippines says there have also been a number of provocative incidents this year near Reed Bank — 85 nautical miles from Palawan and nearly 600 from China.

“China has upped the ante in the past several months and by doing so is undermining its ’peaceful rise’ rhetoric, draining away goodwill and pushing countries in the region closer to the U.S.,” said Storey of Singapore’s ISEAS.

Source: Reuters