After Cambodian troops fired on Thai forces early Monday morning in Ubon Ratchathani province, "the Army received reports that Thai soldiers were attacked with supporting fire weapons, resulting in one soldier killed and four wounded", Thai army spokesman Winthai Suvaree said in a statement.

Winthai also said Thailand had begun "using aircraft to strike military targets in several areas" to suppress attacks by Cambodian forces.

Cambodia's defence ministry spokeswoman Maly Socheata said Thai forces launched an attack on Cambodian troops in the border provinces of Preah Vihear and Oddar Meanchey early Monday morning, accusing Thailand of "firing multiple shots with tanks at Tamone Thom temple" and other areas near Preah Vihear temple.

She said Cambodia did not retaliate.

Met Measpheakdey, a Cambodian spokesman for the Oddar Meanchey provincial administration, said gunfire was reported in the areas of the centuries-old Tamone Thom and Ta Krabei temples, and a "number of villagers who live near the border are fleeing to safety".

Thailand's Second Army Region said in a statement that around 35,000 people in Thailand have been evacuated from areas along the border with Cambodia since the renewed fighting.

The Thai army also accused Cambodian forces of firing BM-21 rockets towards civilian areas in Buri Ram province, with no casualties reported.

Both sides reported a brief skirmish on Sunday, which Thailand's military had said left two soldiers wounded.

Five days of clashes erupted between Thailand and Cambodia this summer, killing 43 people and displacing around 300,000 before a truce took effect.

That cessation of fighting had been brokered in part by the United States, China and Malaysia, the latter as chair of the regional bloc ASEAN.

And in October, US President Donald Trump co-signed a follow-on joint declaration between Thailand and Cambodia, touting new trade deals with the countries after they agreed to prolong the ceasefire.

But Thailand suspended the deal last month after an alleged landmine blast wounded several soldiers.

The two sides then traded accusations of renewed clashes in which Phnom Penh said a civilian was killed.

The dispute centres on a century-old disagreement over borders mapped during France's colonial rule in the region, with both sides claiming a smattering of boundary temples.

burs-sco/mtp