U.S. President Barack Obama attends the East Asia Summit at the Peace Palace in Phnom Penh, Cambodia Tuesday, Nov. 20, 2012. Obama is in Cambodia on the final leg of his three-country tour of Southeast... (Associated Press) 
 
 President Barack Obama's attendance at an annual summit of Southeast Asian leaders on Tuesday thrust him right in the eye of the region's most stormy dispute: the long-raging rivalry between China and five neighbors for control of strategic and resource-rich waters in the South China Sea. 
 
 The inability to resolve these territorial conflicts has become a major impediment to the 10-member Association of Southeast Asian Nations as it tackles ambitious dreams like a plan to turn the economically vibrant region of 600 million people into an EU-like community by the end of 2015. 
 
 Neither the U.S. nor China is a member of ASEAN, but each has strong supporters in the group. Summit host Cambodia, an ally of China, has tried at this week's summit to shift the focus to economic concerns, but Beijing's territorial disputes with its ASEAN neighbors _ including staunch U.S. ally the Philippines _ have yet again overshadowed discussions. 
 
 The disagreement sparked a tense moment Monday when Philippine President Benigno Aquino III challenged Cambodian Prime Minister Hun Sen, who had tried to cut off a discussion of the territorial disputes. 
 
 Into this heated atmosphere came Obama, who flew to Phnom Penh for Tuesday's expanded East Asia Summit, in which the 10 ASEAN countries were joined by eight other nations, including China and the United States. Behind closed doors, the Chinese and Philippine leaders pressed their territorial claims while others called for restraint. After the summit, the exchange shifted to the chandelier-lit lobby, where diplomats of the two countries reiterated their positions. 
 
 Senior Chinese diplomat Fu Ying expressed dismay that the disputes again got the spotlight. "We do not want to bring the disputes to an occasion like this and we do not want to give over-emphasis to the territorial disputes and differences," she said. 
 
 Washington has reiterated that it takes no sides in the territorial disputes but would not allow any country to resort to force and block access to the South China Sea, a vital commercial and military gateway to Asia's heartland. 
 
 Washington has also called for the early crafting of a "code of conduct" to prevent clashes in the disputed territories, a call backed by Australia and Japan, but it remains unclear if and when China will sit down with rival claimants to draft such a legally binding nonaggression pact. 
 
 The potentially oil- and gas-rich South China Sea islands and waters are contested by China, Taiwan and four ASEAN members _ Brunei, Malaysia, the Philippines and Vietnam. 
 
 The last fighting, involving China and Vietnam, killed more than 70 Vietnamese sailors in 1988, and fears that the conflicts could spark Asia's next war have kept governments on edge. 
 
 Vietnam and the Philippines, backed by Washington, have been loudest on the issue, and want China to negotiate with the other claimants as a group. China wants one-on-one negotiations _ which would give it an advantage because of its sheer size and economic clout _ and has warned Washington to stay away from an issue it says should not be "internationalized," a position echoed by Cambodia at the Phnom Penh summit. 
 
 There have been several recent standoffs involving boats and other shows of force, particularly between China and the Philippines, which both claim ownership of the Spratly Islands, a spray of tiny South China Sea atolls. 
 
 Their latest diplomatic confrontation occurred a few hours before Obama touched down Monday in the Cambodian capital, when Hun Sen announced as he was closing a meeting that all ASEAN leaders had agreed not to discuss the divisive issue in talks between the 10-nation bloc and China. 
 
 Alarmed, Aquino raised his hand, stood up and objected to Hun Sen's statement, saying his country, which plans to bring the disputes before a U.N. tribunal, was not party to any such agreement. It was a blunt gesture in the usually servile ambiance of the conservative bloc, an unwieldy collective of rigid, authoritarian regimes and nascent democracies. 
 
 After a brief lull, Hun Sen recovered and said Aquino's remarks would be reflected in the record of the meeting. Still, Cambodian and Chinese officials insisted that the agreement stood. Tensions intensified Tuesday when the Philippines was joined by Vietnam and Singapore in objecting to a plan by Cambodia to state in a post-summit statement by the host country that there was indeed such an agreement, Philippine diplomats said. 
 
 An objection from the Philippines, or any ASEAN nation, ought to be enough to thrash any agreement because the bloc decides by consensus, meaning just one veto from any member kills any proposal. 
 
 "The bottom line is they can talk all they want but if we said we're not with it, there's no consensus, finished," Philippine Foreign Secretary Albert del Rosario told reporters. 
 
 The dispute, and Obama's presence here, highlights how ASEAN has become a major battleground for influence in Asia, just like the South China Sea. The U.S. is pushing its "Pacific pivot" to the region following years of engagement in Iraq and Afghanistan. China, the Asian superpower, has acted to protect its home ground. 
 
 Southeast Asia is clearly pinned in between, and the lack of consensus among the group over the maritime disputes has pushed much of the bloc's other work to the sidelines. 
 
 In July, after a foreign ministers' meeting also hosted by Cambodia, the group failed to publicly issue a traditional after-conference communique _ an embarrassing failure that was a first in ASEAN's 45-year history. Vietnam and the Philippines had insisted that the joint statement simply state that the South China Sea rifts were discussed, but Cambodia adamantly refused, echoing China's line to keep a lid on public discussions of the disputes. 
 
 Ernest Bower of the Center for Strategic & International Studies in Washington, D.C., said the imbroglio in July showed that as long as any ASEAN country remains weak and vulnerable to muscling from a major power, the entire group could be compromised. 
 
 "ASEAN learned a hard lesson from the event," Bower said, "namely, that they should never again allow a fellow ASEAN member country to feel so isolated, exposed or dependent on any foreign power that the country feels compelled to step beyond ASEAN protocols ... in a way that damages the organization's interests and profile." 
 
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 Associated Press writers Grant Peck and Sopheng Cheang contributed to this report. ||||| Image copyright Reuters Image caption Mr Obama (centre) was part of talks between Asian nations that saw discussion of maritime rows and trade pacts 
 
 US President Barack Obama has urged Asian nations to ease tensions over maritime disputes, amid terse exchanges at the end of a summit in Cambodia. 
 
 China and the Philippines openly clashed over who owns islands in the South China Sea, as the East Asia summit came to a close in Phnomh Penh. 
 
 Mr Obama warned against allowing such disputes to escalate. 
 
 Japanese and Australian leaders also attended the meeting, which was part of regional Asean talks. 
 
 The BBC's Jonah Fisher, in Phnomh Penh, says it was an acrimonious end to a summit in which South East Asian countries failed to reach consensus among themselves over how to resolve the various territorial disputes with China. 
 
 Mr Obama's arrival on Monday at the regional talks between the Association of South East Asian Nations (Asean) and other partner countries came amid fractious debate on the maritime row between China and its Asian neighbours. 
 
 The Scarborough Shoal, or Huangyan islands as they are called in China, were at the centre of a stand-off between China and the Philippines earlier this year. 
 
 On Tuesday the US president met Chinese Premier Wen Jiabao but did not refer to the row in public comments. 
 
 The "co-operative and constructive approach" the US and China had taken to ties served both countries, Mr Obama said, but "clear rules of the road" were needed for international trade. 
 
 Mr Wen, for his part, said economic co-operation would be enhanced "as a means to tackle the difficulties we have and resolve the difference and disagreements between us". 
 
 Asia is one part of the world that still has economic growth, and the American recovery depends on that continuing. The president is trying to establish various free-trade agreements with countries in the region. Asia is also the arena for a struggle between the world's only two super-powers - ideology and power are at stake. 
 
 Both sides ignored shouted questions from reporters about the South China Sea, AFP news agency said. 
 
 "President Obama's message is there needs to be a reduction of the tensions," deputy National Security adviser, Ben Rhodes, said after the summit. 
 
 "There is no reason to risk any potential escalation, particularly when you have two of the world's largest economies - China and Japan - associated with some of those disputes." 
 
 China claims a U-shaped swathe of the South China Sea, including areas also claimed by Vietnam, the Philippines, Malaysia and Brunei. 
 
 Tensions have been high with Manila and Hanoi in recent months amid stand-offs and minor clashes around shoals and islands disputed with China. 
 
 The last Asean summit in July broke up acrimoniously, without a joint communique, with China facing accusations of using its clout to force host Cambodia to keep the territorial issue off the agenda. 
 
 Tensions continued at the latest summit. Cambodia said on Sunday that Asean nations had agreed not to "internationalise" the issue, something Beijing has been pushing for. 
 
 But on Monday, the Philippines - which has been boosting ties with the US - said no such accord had been reached and that it had "the inherent right to defend its national interests when deemed necessary". 
 
 The Philippines lodged a formal protest against Cambodia, saying that it was trying to contain discussions on the matter. 
 
 China said it did not want to bring the disputes to such a forum. "We do not want to give over emphasis to the territorial disputes and differences, and we don't think it's a good idea to spread a sense of tension in this region," Wen Jiabao told the summit, according to Chinese Deputy Foreign Minister Fu Ying. 
 
 Japanese Prime Minister Yoshihiko Noda also raised security concerns in a meeting with Mr Obama. Japan is currently embroiled in a separate territorial dispute with Beijing over islands in the East China Sea. 
 
 "With the increasing severity of the security environment in East Asia, the importance of the Japan-US alliance is increasing," Mr Noda said. 
 
 Trade moves 
 
 Discussions at the summit also focused on at least three free trade pacts in the region. 
 
 Officials from China, Japan and South Korea met on the sidelines to start talks on the possibility of a free-trade zone, the three countries said in a joint statement. 
 
 Asean countries and China, Japan, South Korea, India, Australia and New Zealand have also launched negotiations for the Regional Comprehensive Economic Partnership (RCEP) trade pact, which seeks to strengthen regional trade. 
 
 The US also led the Trans-Pacific Partnership (TPP) negotiations which currently involve four countries from Asean - Singapore, Brunei, Malaysia and Vietnam. 
 
 Mr Obama arrived in Cambodia from Burma, where he spent six hours meeting top leaders. 
 
 The first visit to the country by a serving US president, it was seen as a response to reforms initiated by the government of President Thein Sein.
– President Obama is in Cambodia today, meeting with East Asian leaders amid a contentious territorial dispute over the South China Sea. Speaking publicly, neither Obama nor Chinese Premier Wen Jiabao responded to reporters' shouted questions about the tensions, the BBC reports. Instead, Obama referred to a "cooperative and constructive approach" to relations between the US and China, though he cited a need for "clear rules of the road" on trade. But the summit (which joins the 10 ASEAN countries with eight other nations, including China and the US) was expected to focus on the territorial issues. To wit, the AP reports that behind closed doors, the Chinese and Philippine leaders pressed their territorial claims while others called for restraint. Those two countries, along with Taiwan, Vietnam, Malaysia, and Brunei, all have claims to a portion of the South China Sea, while China and Japan disagree over control of islands in the East China Sea. Trade talks between the East Asian countries, as well as Australia and New Zealand, were expected to be another focus of the summit.