Japan warned on Monday that a row over the South China Sea could directly influence "peace and stability" in Asia as the Philippines publicly disagreed with Cambodia over the contentious territorial issue at a regional summit.
Wading into one of Asia's most divisive and vexing security problems, Japanese Prime Minister Yoshihiko Noda challenged efforts by summit host Cambodia to limit discussions on the South China Sea, where China's territorial claims overlap those of four Southeast Asian countries and of Taiwan.
"Prime Minister Noda raised the issue of the South China Sea, noting that this is of common concern for the international community, which would have direct impact on peace and stability of the Asia-Pacific," a Japanese government statement said after Noda met leaders from the 10-member Association of Southeast Asian Nations (ASEAN).
That followed a statement on Sunday from Kao Kim Hourn, a Cambodian foreign ministry official, who said Southeast Asian leaders "had decided that they will not internationalise the South China Sea from now on."
In a sign of tensions within Southeast Asia over Chinese sovreignty claims, Philippine President Benigno Aquino disputed the Cambodian statement and said no such agreement had been reached, voicing his objections in tense final minutes of discussions between Noda and Southeast Asian leaders.
As Cambodian Prime Minister Hun Sen began to conclude the meeting, Aquino abruptly raised his hand and tersely interjected.
"There were several views expressed yesterday on ASEAN unity which we did not realise would be translated into an ASEAN consensus," he said, according to his spokesman. "For the record, this was not our understanding. The ASEAN route is not the only route for us. As a sovereign state, it is our right to defend our national interests."
Alternative diplomatic routes for the Philippines would likely involve the United States, a close ally. Cambodia, on the other hand, has deep ties with China.
U.S. President Barack Obama will meet Southeast Asian leaders on Monday evening before sitting down with Chinese Premier Wen Jiabao on Tuesday. He is widely expected to raise the issue of South China Sea tensions.
China has repeatedly sought to reject involvement by nations outside Southeast Asia at a sensitive time, as Washington seeks an expanded military and diplomatic presence in the region under a so-called "pivot" from conflicts in the Middle East and Afghanistan announced last year.
China's assertion of sovereignty over the stretch of water off its south coast and to the east of mainland Southeast Asia has set it directly against U.S. allies Vietnam and the Philippines, while Brunei, Taiwan and Malaysia also lay claim to parts, making it Asia's biggest potential military trouble spot.
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The Philippines, Australia and other parts of the region have seen a resurgence of U.S. warships, planes and personnel since Obama began shifting foreign, economic and security policy towards Asia late last year.
Cambodia has used its powers as ASEAN chair this year to limit discussion on the South China Sea, in line with Beijing's view the disputes should be discussed on a bilateral basis.
Kao of the Cambodian foreign ministry said on Sunday the ASEAN bloc had agreed to confine talks on a set of rules for operating in the South China Sea to its meetings with China.
Philippine Foreign Secretary Albert Del Rosario, however, told reporters that Vietnam shared the Philippines' objections to that Cambodian statement. Vietnam officials were not immediately available to confirm that.
The tensions illustrate the difficulty of forging a Southeast Asian consensus over how to deal with an increasingly assertive China. Southeast Asia had hoped avoid a repeat of an embarrassing breakdown of talks in July over competing claims in the mineral-rich waters, its biggest security challenge.
Washington insists its "pivot" is not about containing China or a permanent return to military bases of the past, but it has increased its military presence in the Philippines and other areas near vital sea lanes and border disputes in the South China Sea that have raised tensions with China.
Cambodian Information Minister Khieu Kanharith said Hun Sen had discussed the issue with China's Wen on Sunday evening but did not provide details. However, he said "China wants a peaceful resolution."