US Expert Says Thailand–Cambodia Conflict Raises Legal, Humanitarian Concerns

PHNOM PENH, Cambodia (Dec. 16, 2025) — As fighting continues along the Thailand–Cambodia border, questions of legality and proportionality under international law are coming into focus, according to American analyst Arnaud Darc.

Darc told reporters that public debate has largely centered on “who fired first,” but under international law that is only the starting point. He said legality is determined by limits and thresholds, not rhetoric.

Citing official statements and independent reporting from Reuters, the Associated Press, the BBC, the United Nations and the International Committee of the Red Cross, Darc said Thailand’s military actions raise serious legal questions, particularly its claim of self‑defense under Article 51 of the UN Charter.

Thailand has formally invoked its right to self‑defense, but Darc noted international law requires five criteria: armed attack, clear attribution, necessity, proportionality and immediacy. Independent sources have not verified which side initiated hostilities Dec. 7–8, leaving Thailand with the burden of proof.

Reports of deep incursions, air power and economic measures suggest Thailand’s campaign may extend beyond immediate defense into sustained coercion, Darc said.
He stressed that humanitarian law applies regardless of who fired first. More than half a million people have been displaced, with civilian deaths reported on both sides.

Cambodia has alleged airstrikes near displaced civilian camps and operations in Siem Reap province, though these claims have not been independently verified.

Darc urged independent monitoring, satellite confirmation and humanitarian access to prevent escalation. “International law still provides a framework to contain this conflict,” he said. “But it only works if states accept limits and allow facts to be independently verified.”