PHNOM PENH, Cambodia (AP) — Cambodia’s government has filed notice under a U.N. agreement on maritime law for compulsory conciliation of a sea border dispute with neighboring Thailand, Prime Minister Hun Manet said Tuesday.

At issue is territory claimed by both that is believed to contain large, exploitable amounts of natural gas and other hydrocarbons.

The decision to take the matter to the the U.N. Convention on the Law of the Sea, or UNCLOS, comes after Thailand last month terminated a 25-year-old memorandum of understanding with Cambodia meant to resolve overlapping maritime claims.

Thailand unilaterally revoked the agreement in May after relations between the countries worsened last year after major armed clashes over their land border.

Last year’s fighting with Cambodia spurred nationalistic fervor, putting political pressure on Thai Prime Minister Anutin Charnvirakul to abrogate the pact.

In a live broadcast on TVK state television, Hun Manet said that his government had delivered formal notice to Thailand and to the U.N. secretary-general to begin compulsory conciliation proceedings under UNCLOS rules.

“Cambodia has never violated the sovereignty of other states,” he said.

“At the same time, we are unwaveringly determined to defend Cambodia’s sovereignty. Today, we continue to honor that responsibility, not through force, but through international law; not through unilateral action, but through peaceful engagement.”

It wasn’t immediately clear when the claim might be adjudicated.

Anutin responded to the announcement by telling reporters that Cambodia’s action wasn’t a problem. He had previously said that Thailand would continue to pursue a resolution of the maritime border issue according to UNCLOS guidelines, but didn’t agree with Cambodia’s intention to force conciliation.

Any UNCLOS ruling isn’t binding on the parties involved, even though both countries are signatories to the international pact.

Thailand has been averse to having territorial issues decided by third parties rather than handled bilaterally. It has long felt that a 1962 ruling by the International Court of Justice awarding Cambodia the hilltop Preah Vihear temple along their border to be unfair, which has contributed to ongoing tensions between the neighbors.