Disputes over South China Sea territories are expected to overshadow a summit of Southeast Asian countries that opened Saturday, with host Cambodia seeking damage control after the previous regional meeting it hosted collapsed over how to handle the territorial conflicts involving China.

President Barack Obama will join the summit on Tuesday in his first appearance on the world diplomatic stage since his re-election. His Southeast Asian trip - which is to include the first visit to Myanmar by a U.S. president - will highlight America's pivot to the economically vibrant region as a counterweight to China's rapid rise, but is also likely to see him tread on a tightrope over delicate regional issues like the territorial rifts and human rights.

Foreign ministers of the 10-member Association of Southeast Asian Nations, or ASEAN, met at a convention center in the Cambodian capital of Phnom Penh, where about 10,000 troops and police were deployed to guard the biggest international gathering the country has hosted in recent history. Army commandos, armed with machine guns and donning knee and elbow pads, prowled around the venue.

ASEAN heads of state will gather Sunday before meeting with dialogue counterparts from eight countries, including China and the United States.

Founded as an anti-communist club in 1967 during the Cold War era, ASEAN prides itself on having united an unwieldy collective of liberal democracies and authoritarian states in one regional bloc. But the grouping - which has been tested by all sorts of crises and disputes - unraveled at another regional summit last July when host Cambodia tangled with Vietnam and the Philippines on the handling of the South China Sea issue.

Cambodia, which has long been economically dependent on China, refused to allow mention of the territorial disputes in a post-ministerial conference communique as demanded by Vietnam and the Philippines, sparking a high-profile verbal squabble. The rift scuttled the issuance of any communique in an unprecedented moment of disunity in ASEAN's 45-year history.

China, which has been locked in the disputes with the Philippines, Vietnam and three other governments, has tried in vain to keep the conflicts from international forums such as ASEAN. The Philippines and Vietnam, with the backing of Washington, have opposed China's stance and taken steps to raise international awareness of the problem, which they said could threaten the stability and freedom of navigation in the South China Sea, through which a major bulk of the world's oil and cargo passes.

ASEAN Secretary-General Surin Pitsuwan said governments under the bloc have realized they would have to forge a common ground on touchy issues to protect the organization just three years before an ambitious plan to turn the region of 600 million people into an E.U.-like community that could compete with Asian powerhouses such as China and India.

"All sides realize that we must move from the agenda of contention and confrontation to an agenda of cooperation," Surin told The Associated Press.

Still, concerns over a lack of a clear prospect of immediately ending the worrisome territorial conflicts were palpable. Indonesian Foreign Minister Marty Natalegawa proposed that ASEAN member countries and China establish emergency hotlines to allow officials to rapidly contain any outbreak of violence in contested South China Sea areas as a diplomatic resolution remains elusive.

While all the rival claimants - China, Brunei, Malaysia, the Philippines, Taiwan and Vietnam - have pledged to peacefully resolve their disputes, Natalegawa feared an accidental clash could get out of hand if governments did not have lines of communications devoted to rapidly contain any outbreak of violence.

"The real challenge for us is miscalculation, misunderstanding, misperception," he told reporters late Friday.

The disputes have long been feared as Asia's next potential flashpoint.

Obama and his Philippine and Vietnamese counterparts are expected to separately reiterate the need to ensure the disputes do not destabilize the region and block access to the South China Sea, which Beijing has claimed in its entirety.

Japanese Prime Minister Yoshihiko Noda is also expected to raise his country's separate territorial problem with China, which recently flared.

During the summit, ASEAN leaders are scheduled to sign a document adopting a nonbinding regional declaration to protect human rights, which diplomats have praised as a milestone in a region notorious for violations. U.N. officials and rights watchdogs have criticized the pact, saying it falls below international standards.

Capping the summit on Tuesday will be a ceremony to launch the start of negotiations for an expanded free-trade area that will group all ASEAN members, along with China, Japan, South Korea, India, Australia and New Zealand. The 16-country pact will initially exclude the United States, which has been promoting a separate accord to integrate Asia-Pacific economies.

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Associated Press writer Grant Peck contributed to this report.