Troops from Thailand and Cambodia exchanged fire at a disputed portion of their border early on Thursday, both sides said.
The Thai military said Cambodian soldiers opened fire near the Khmer temple Ta Muen Thom, where tensions have run high in recent weeks.
Cambodia’s defence ministry however said Thai troops fired the first shots, and Cambodian soldiers responded in self-defence.
Cambodia had sent a surveillance drone into the area before deploying troops carrying heavy weapons, the Thai military said.
A spokeswoman for the Cambodian defence ministry, Maly Socheata, said their troops “exercised their right to defend their sovereignty and territorial integrity against the aggression of the Thai troops.
Socheata said Thailand “violated the territorial integrity of Cambodia”.
The clash on Thursday morning comes hours after Thailand recalled its ambassador to Cambodia, following a landmine explosion that injured a Thai soldier along the border.
On Wednesday, Bangkok also said it would expel Cambodia’s ambassador.
Bilateral relations between the two countries are at their worst in more than a decade, after armed clashes in May left one Cambodian soldier dead.
In the past two months, both countries have imposed tit-for-tat restrictions and strengthened troops presence along the border.