Southeast Asia will not issue a statement on the rejection of Chinese territorial claims in the South China Sea by an international tribunal, regional diplomats said Thursday, blaming the no-comment on pressure by Beijing.

The Association of Southeast Asian Nations (ASEAN) had weighed whether to speak out on Tuesday's ruling by the Permanent Court of Arbitration in The Hague, said Southeast Asian diplomats with knowledge of the matter.

But 10-member ASEAN, whose unity has been increasingly strained in the face of Chinese expansionism, could not find common ground, they said.

"ASEAN officials had prepared a draft text but there was no agreement to release a joint statement," said a Southeast Asian diplomat, adding that China was believed to have leaned on its ASEAN allies Laos and Cambodia to prevent a statement in the highly charged affair.

"Some ASEAN countries are definitely not happy. Beijing's action can be seen as interference in ASEAN's centrality," the source said.

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Another senior Southeast Asian diplomat said China has "succeeded in splitting ASEAN through its allies on the South China Sea issue," referring to Laos and Cambodia.

Chinese pressure was blamed last month for a startling diplomatic U-turn by ASEAN, which swiftly disowned a joint statement released by Malaysia after an ASEAN-China meeting.

That statement had expressed alarm over Beijing's activities in the South China Sea. The fiasco highlighted the bloc's inability to maintain a united front on the issue.

China claims nearly all of the strategic sea -- home to some of the world's most important shipping routes -- and has steadily strengthened its toehold by converting reefs and sandbars into islands.

The Philippines brought an international arbitration case over China's growing assertiveness, resulting in this week's thorough repudiation of Beijing by the Hague tribunal, which said Chinese claims had no legal basis.

China has in turn rejected the ruling and reiterated its positions.

ASEAN members the Philippines, Vietnam, Malaysia and Brunei, as well as Taiwan, have competing claims to parts of the resource-rich sea.

While the Philippines and Vietnam have been particularly critical of China, Laos and Cambodia are generally regarded as preferring to side with their giant neighbour and benefactor.

Laos holds ASEAN's chair this year.

Asked about the lack of an ASEAN statement, Philippine foreign affairs department spokesman Charles Jose said Thursday: "Kindly direct your query to the chairman, Laos, because it is the one consolidating views and positions, being the chair."

Cambodia had said before this week's ruling that it would not back any ASEAN comment, effectively ruling out a statement since the bloc doesn't speak without full consensus.

ASEAN has in recent years released joint statements expressing increasing alarm over South China Sea island-building, while taking care not to single out China.

But those days may be over given the issue's potential to divide ASEAN, said former Philippine UN representative Lauro Baja.

"We should no longer expect in the future that there will be an ASEAN statement on China," Baja said.