Foreign ministers from the 10-member Association of Southeast Asian Nations (ASEAN) failed to release a joint statement as scheduled on Saturday evening, and tense follow-up negotiations the next morning could still not end the stand-off, two diplomats involved in the talks told AFP.
China claims nearly all of the South China Sea, including waters approaching the coasts of ASEAN members Vietnam, the Philippines, Malaysia and Brunei.
The tense talks came after Vietnam, which also claims parts of the strategically vital sea, insisted that tough language be inserted into the statement expressing concern over Chinese land reclamation in the contested waters.
Cambodia, one of China's strongest allies within ASEAN, had firmly resisted, according to the diplomats involved in the talks in the Philippine capital, as well as an excerpt of proposed Cambodian resolution obtained by AFP on Sunday.
"Vietnam is adamant and China is effectively using Cambodia to champion its interests," one of the diplomats said.
"But the Philippines is trying very hard to broker compromise language."
China has in recent years expanded its presence in the sea by building artificial islands, which are capable of holding military bases.
While senior officials pressed on with negotiations on the sea dispute Sunday, ASEAN foreign ministers went into a round of separate meetings with their counterparts from China, the United States and other Asia-Pacific nations.
ASEAN and China were due to approve a framework for a code of conduct in Manila on Sunday on how to deal with sea dispute.
Analysts have cautioned not to place too much significance on the agreement on a framework.
They say it comes 15 years after negotiations on the issue first began, and China has used that time to cement its claims with the artificial islands, while an actual code likely remained many years away.
Diplomats said they were still hoping the joint ASEAN statement meant to be released on Saturday would be agreed on before all the other meetings hosted by the bloc ended on Tuesday.
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