Southeast Asian nations called for self-restraint on territorial disputes in the South China Sea as tensions escalate over China’s pursuit of its claims to large swaths of the resource-rich region.

Leaders called on all parties to “refrain from taking actions that would further escalate tension,” in a statement issued at the end of the 10-member Association of Southeast Asian Nations meeting yesterday in Naypyidaw in Myanmar. They called for progress on a code of conduct that would seek to preserve freedom of navigation in the area, through which some of the world’s busiest shipping lanes run.

Disputes are mounting as Asian neighbors push back against Chinese moves to assert control over the maritime areas. Its placement of an oil rig near the disputed Paracel Islands led last week to clashes between Vietnamese and Chinese boats, while the Philippines detained 11 Chinese fisherman in a contested area. Vietnamese protested in several cities yesterday against China’s actions.

The escalation risks spilling over to separate territorial disputes between Japan and China in the East China Sea. Russia has recently stepped up air patrols around parts of North Asia, adding to the pressure.

“Japan will surely take advantage of the South China Sea tensions to advocate its ‘China Threat Theory’,” according to Liu Jiangyong, a professor at the Institute of International Studies at Tsinghua University in Beijing. “Japan will likely support or aid Vietnam and the Philippines in challenging China and make the situation even worse,” Liu said by phone.

China’s actions come after President Barack Obama’s visit last month to Asia to reassure allies of the U.S. commitment to its strategic rebalance to the region. Still, Obama said the U.S. was not seeking to contain or control China and, speaking in Manila, he said the focus of U.S. foreign policy had shifted from deploying combat troops to “avoiding errors.”

“I’m sure some in China are keen to see how far they can go,” said Mark Beeson, professor of international politics at Murdoch University in Perth. “The big question is whether this is a coordinated, top-down policy approved by Xi Jinping,” or “whether there’s quite a bit of ad hoc policy freelancing by the PLA and provincial governments,” he said, a reference to the People’s Liberation Army.

President Xi is expanding China’s naval reach to back its claims to the South China Sea that are based on the “nine-dash line” map, first published in 1947. That claim extends hundreds of miles south from China’s Hainan Island to equatorial waters off the coast of Borneo. China and Vietnam both claim the Paracel Islands, and Asean members Brunei, Malaysia and the Philippines have claims to other areas.

Still, the statement from Asean foreign ministers touching on the disputes is not a major achievement for the grouping, according to Beeson. “There’s clearly some reluctance on the part of some members to do anything to upset China and very little real solidarity or common purpose beyond face saving,” he said by e-mail.

The matter isn’t between China and Asean, the official Xinhua News Agency cited Chinese Foreign Ministry spokeswoman Hua Chunying as saying May 10.

“The Chinese side is always opposed to one or two countries’ attempts to use the South Sea issue to harm the overall friendship and cooperation between China and the Asean,” Hua said.

Southeast Asian foreign ministers separately met on May 10 in Naypyidaw and said afterward in a statement that South China Sea claimants should “avoid actions which could undermine peace and stability in the area.”

Asean is seeking a code of conduct for the waters, with talks making little progress since China agreed in July to start discussions, and China introducing fishing rules in January requiring foreign vessels to seek permission before entering waters off its southern coast.

Asean foreign ministers view the tensions as a matter of “grave concern,” Singapore Foreign Minister K. Shanmugam told reporters. “Asean needs to be neutral, but Asean cannot stay silent,” he said. “For the benefit of the entire region, there has to be peace. There should be no mishaps. Mishaps can easily get out of hand. And tensions, mishaps, incidents, if they result in the disputes becoming larger, it’s bad for all of us.”

Philippine Foreign Affairs Secretary Albert Del Rosario said he was satisfied with the Asean statements, neither of which referred specifically to China.

“We are united and we are projecting centrality,” he told reporters yesterday. “The expression of the situation there is descriptive enough.”

Vietnam’s Prime Minister Nguyen Tan Dung called on Asean members to support it over the territorial dispute.

“Vietnam has practiced restraint, showed goodwill and used all dialogue channels with China at different levels to protest and demand China remove the oil rig and military ships from Vietnam’s waters,” he said in a speech at the summit. Vietnam “will resolutely protect its national sovereignty and legitimate interests.”

Deputy Foreign Minister Pham Quang Vinh separately told reporters that Vietnam prized its “friendly and good” relationship with China and sought to resolve the dispute in accordance with international law.

Asean’s statements on the disputes could affect China’s trust in the group, according to Xu Liping, senior fellow at the National Institute of International Strategy at the Chinese Academy of Social Sciences in Beijing.

“China always rejects internationalization and Asean- lization of the South China Sea disputes,” Xu said by e-mail. “The prerequisite of making a code of conduct is mutual trust. Without mutual trust, there is not any cooperation.”

Vietnam on May 7 said Chinese boats rammed its vessels, fired water cannons and used low-flying aircraft in a confrontation over the oil rig. China the next day accused Vietnamese ships of provoking the clash by crashing into its boats.

About 1,000 people marched in Ho Chi Minh City yesterday while hundreds gathered in a public square in front of the Chinese embassy in the capital city of Hanoi.

“We don’t want to have war, but we don’t want them to come here to take our land,” said Nguyen Van, a 42 year-old office worker wearing a shirt with the Vietnamese flag as she spoke in Ho Chi Minh City before the protest marches started. “We wish to stand up and protect our land, as our parents did.”

The confrontation off Vietnam’s coast is the most serious between the two countries since 2007 when Chinese naval patrol vessels fired on a Vietnamese fishing boat, killing one sailor. In 1988, a Chinese naval attack in the Spratlys, which Vietnam also lays claims to, killed 64 Vietnamese border guards as China seized seven atolls.