The hearing at the Singapore outpost of the Permanent Court of Arbitration (PCA) comes after the countries fought two rounds of deadly border clashes last year.

In May this year, Thailand unilaterally pulled out of a framework agreement with Cambodia that aimed to resolve overlapping maritime border claims, but denied any link to their land dispute.

Cambodia subsequently initiated a UN-backed conciliation process at the PCA, saying it hoped to return to constructive negotiations.

Opening Bangkok's case before a five-member panel of international legal experts, Foreign Minister Sihasak Phuangketkeow said Cambodia sought to "vilify Thailand through false narratives, distortion of facts, and unfounded accusations [...] including at international forums".

"It does this by playing the role of a victim with a sense of self-righteousness aimed at claiming the moral high ground," he said.

Last year's clashes left dozens of people dead and displaced more than a million before a truce was agreed.

Thailand has said it withdrew from the framework agreement, called "MoU 44", because "no progress had been made" in implementing it. Prime Minister Anutin Charnvirakul denied the move was linked to the fighting.

The 2001 memorandum of understanding covers a resource-rich maritime territory of around 27,000 square kilometers to which both Cambodia and Thailand lay claim.

Cambodia said last week that it had resorted to conciliation "after Thailand unilaterally terminated the agreed bilateral framework" through which the two nations had "negotiated their overlapping maritime claims for more than two decades".

Prime Minister Hun Manet said in June that the move was also to "protect Cambodia's sovereignty and maritime rights in accordance with international law".

Foreign Minister Prak Sokhonn told the PCA panel on Tuesday that Phnom Penh saw the process "as a means to rebuild trust, not as a form of escalation".

Cambodia's goal was to agree with Thailand on a "single, all-purpose maritime boundary", or alternatively agree to jointly develop and equitably share resources until a boundary is drawn, he said.

"Cambodia sincerely hopes that Thailand will engage constructively in this process."

Sihasak said Thailand was also seeking maritime delimitation and to rebuild trust.

Set up in 1899, the PCA is the world's oldest intergovernmental dispute-resolution body and resolves disputes between countries and private parties by referring to contracts, special agreements and various treaties, such as the UN Convention on the Law of the Sea.

The PCA office in Singapore is the Hague-based court's first in Asia.

The commission's recommendations are not binding and will take about a year to be decided.

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