Days of heated diplomacy ended in failure as splits over territorial disputes with China prevented Southeast Asian nations from issuing their customary joint statement at a summit on Friday.
Foreign ministers from the 10-member Asean bloc have this week tried to hammer out a final communique in Cambodia, which has held up progress on a draft code of conduct aimed at soothing tension in the flashpoint South China Sea.
China claims sovereignty over nearly all of the resource-rich sea, which is home to vital shipping lanes, but the Philippines, Vietnam, Malaysia and Brunei among others have competing claims in the area.
The Philippines lambasted the failure at the summit, saying "it deplores the non-issuance of a joint communique... which was unprecedented in Asean's 45-year existence".
It had insisted Asean refer to a stand-off in June with China over a rocky outcrop known as the Scarborough Shoal, but Cambodia -- a Beijing ally and chair of the meeting -- resisted.
Taking "strong exception" to Cambodia for opposing mention of the shoal, the Philippine statement said divisions undercut previous Asean agreements on tackling disputes as a unit, "and not in a bilateral fashion -- the approach which its northern neighbour (China) has been insisting on".
China is a key bankroller of Cambodia and some diplomats said Phnom Penh had played Beijing's hand at the summit by blocking a communique mentioning specific alleged infringements.
Cambodian foreign minister Hor Namhong expressed regret at the discord within the organisation, but said he could "not accept that the joint communique has become the hostage of the bilateral issue (between the Philippines and China).
US Secretary of State Hillary Clinton, who joined the summit on Thursday, had expressed hope of Asean unity and had urged progress on the code of conduct, which is seen as reducing the chances of conflict in the South China Sea.
Analysts said the friction could "contaminate" future negotiations between Asean and China.
"Cambodia is showing itself as China's stalking horse. This will make negotiating a final code of conduct with China more difficult," said Southeast Asia expert Carl Thayer, who runs a consultancy.
"I find it difficult to believe that Asean foreign ministers cannot come up with some formulation that satisfies all parties."