Deadly clashes erupted along the Thai-Cambodian border, killing at least 11 civilians and one soldier, all on the Thailand side, as a diplomatic crisis deepens between the Southeast Asian neighbours.

Violence intensified on Thursday when both nations exchanged gunfire, with accusations of who initiated the fighting. Diplomatic ties have severely deteriorated since Wednesday, leading Thailand to seal all land border crossings with Cambodia.

The situation has been worsening since a May confrontation that killed one Cambodian soldier, with nationalist sentiments inflaming tensions on both sides.

Thai military sources reported the heaviest casualties in Si Sa Ket province, where six people died during an attack on a petrol station. At least 14 others sustained injuries across three border provinces.

The fighting escalated as Thai forces launched air attacks against Cambodian military positions, while Cambodia reported Thai jets bombing a road near the historic Preah Vihear temple.

Thai Ministry of Defence spokesperson Surasant Kongsiri confirmed ongoing fighting in at least six border areas. Thursday’s initial clash occurred near the ancient Ta Muen Thom Temple on the border between Thailand’s Surin province and Cambodia’s Oddar Meanchey province.

Cambodian Prime Minister Hun Manet declared that while his nation has consistently pursued peaceful solutions, “we have no choice but to respond with armed force against armed aggression”.

Earlier on Thursday, Cambodia downgraded diplomatic relations with Thailand to their lowest level, expelling the Thai ambassador and recalling all Cambodian embassy staff from Bangkok. This action followed Thailand’s withdrawal of its ambassador and expulsion of the Cambodian ambassador on Wednesday in protest of a landmine explosion that injured five Thai soldiers.

Regarding Thursday’s initial confrontation, the Thai army reported that it detected an unmanned aerial vehicle before spotting six armed Cambodian soldiers approaching Thailand’s position. Despite Thai soldiers’ verbal attempts to defuse the situation, the Cambodian forces allegedly opened fire first.