The dispute centers on a 26,000-square-kilometer area in the Gulf of Thailand believed to contain significant oil and natural gas reserves estimated to be worth about $300 billion. Both countries have claimed the area for more than 25 years.

Cambodia this week launched a compulsory conciliation process under the United Nations Convention on the Law of the Sea (UNCLOS) after Thailand ended a 2001 framework agreement governing negotiations over the contested maritime zone.

Thai Foreign Minister Sihasak Phuangketkeow said Bangkok would appoint two representatives to participate in the UN-backed process but criticized Cambodia’s decision to move ahead with arbitration rather than continue bilateral negotiations.

Cambodian Foreign Minister Prak Sokhonn defended the move, saying direct talks had been exhausted and expressing hope that Thailand would engage constructively in the process.

Thai Prime Minister Anutin Charnvirakul said Thailand would halt all other negotiations with Cambodia, including talks related to land-border issues, and maintain the closure of border checkpoints.

Relations between the neighbors have remained strained since deadly border clashes last year that killed nearly 150 people and displaced more than 300,000, although a ceasefire agreed in December remains in place.

The UNCLOS conciliation process involves a five-member panel that issues non-binding recommendations. It has been used successfully only once before, when Timor-Leste and Australia resolved a decades-long maritime dispute.