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For 49 years, the unity of Southeast Asia's main grouping has hinged on its founding principle: decisions by consensus. But that cardinal principle is now proving to be the biggest headache for its members, who began important meetings Saturday deeply divided on how to deal with China's territorial expansion in the South China Sea.

After preparatory meetings of senior officials, the foreign ministers of the 10 members of the Association of Southeast Asian Nations will gather Sunday for talks that are expected to focus on the economy, terrorism, security, cybersecurity and transnational cooperation. This will be followed by a series of talks in the following days with the United States, China, Japan, South Korea, Russia, India, Australia and New Zealand.

While the agenda of the meetings is extensive, the focus behind the scenes is expected to be on the July 12 decision by a Hague-based tribunal in a dispute between China and the Philippines. The Permanent Court of Arbitration found that China had no basis for the expansive claims it has made on territorial waters around the Philippines. China has similar claims against other ASEAN nations, including Vietnam and Malaysia, and the ruling should have emboldened the grouping to challenge China more forcibly.

One avenue for ASEAN to show its teeth is at its foreign ministers' meeting, through a joint statement at the end.

Easier said than done, however, with the nagging consensus principle getting in the way. Laos, which has assumed the rotating chairmanship of ASEAN this year, is a staunch China ally and is unlikely to allow an open slap by other regional colleagues on a trusted friend. By its side is Cambodia, another China ally.

Including a reference to the tribunal's ruling in the final communique "is a difficult issue that requires efforts of all parties," said Tran Viet Thai, deputy director of the Institute of Strategic Studies, a Vietnamese government think-tank.

Still, ASEAN will have to make a statement on the ruling, Thai said. "They cannot avoid it at such a major and international event," he said. "The issue is how Laos will play their host role and how other countries contribute to the success of the meetings."

Thai described the tribunal's ruling as very important because, theoretically at least, it should help resolve disputes, uphold the law and clarify the stance of the various parties. "But at this point, it is not a magic stick ... it's not a solution to everything, but rather it needs to be combined with other measures," he said.

The South China Sea is dotted with reefs and rocky outcroppings that several governments claim, including China and the Philippines. The arbitration panel didn't take a position on who owns the disputed territories. It did conclude that many of them are legally rocks, even if they've been built into islands, and therefore do not include the international rights to develop the surrounding waters. That and other findings invalidated much of what China's called its historic claims to the resource-rich sea.

In order to ease tensions, China, the Philippines and possibly other claimants must define what the ruling means for fishing, offshore oil and gas exploration, and military and other activities in the vast body of water that lies between the southern Chinese coast and the Philippine archipelago.

Other analysts said one should not place too much importance on ASEAN's position, and focus more on how to enforce the tribunal's rulings.

"We therefore should not pay too much attention to whether the ASEAN meetings will or will not issue a final communique," said Tran Cong Truc, a former head of Vietnam's borders committee. "We instead should pay more attention on what to do next and how we can sit together to settle disputes by peaceful means."

China has already rejected such a meeting, and called for bilateral negotiations with the Philippines. In recent days, its military has staged live-firing exercises in the area and said it would begin regular aerial patrols over the sea. It also has asserted that it will not be deterred from continuing construction of its man-made islands in the South China Sea.

The Philippines also remains in a tight spot despite the legal and moral victory it gained through the tribunal's decision. It simply cannot afford to antagonize China, especially since the Philippines' new president, Rodrigo Duterte, has made friendly overtures to Beijing already to repair relations that were strained severely under the administration of his predecessor, Benigno Aquino III.

But if Duterte appears too soft on China, he will face anger at home and will also come under pressure from the U.S. and Japan, also key allies. In the final months of the Aquino presidency, the Philippines tried to get all ASEAN member states to agree to issue a joint statement of support to the then-impending arbitration ruling. Cambodia and Laos, expectedly, refused to sign on.

The foreign ministers of China and the Philippines are likely to hold separate bilateral meetings in Vientiane this coming week. If they find common ground, the Philippines will prioritize the issue of access for Filipino fishermen in the disputed Scarborough Shoal.

Since 2012, the fishermen have been blocked by Chinese coast guard ships from the disputed shoal, located off the northwestern Philippines. The tribunal ruled that Scarborough is a traditional fishing area that's open to Chinese and Filipinos, and that China violated the Filipinos' maritime rights when it barred them from fishing there.

Malaysia also remains concerned about a report by its navy of Chinese movement that may indicate it may be preparing to undertake dredging in Luconia Shoal, where a Chinese coast guard ship has had a presence for more than two years.

The upcoming meetings will also be notable for the presence of Myanmar Foreign Minister Aung San Suu Kyi, who will be attending an ASEAN meeting for the first time in that role since her party took power earlier this year after decades of military rule.

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Associated Press writers Minh V. Tran in Hanoi, Vietnam, and Jim Gomez in Manila, Philippines, contributed to this report.