Thailand’s army said on Tuesday its Cambodian counterpart claimed fresh cross-border fire was an accident, after Bangkok accused Cambodian forces of violating a 10-day-old truce with a strike that wounded a soldier.

The decades-old dispute between the Southeast Asian neighbours erupted into military clashes several times last year, with fighting in December killing dozens of people and displacing around one million on both sides.

The two countries agreed a truce on December 27, ending three weeks of clashes.

“Cambodia has violated the ceasefire” on Tuesday morning, the Thai army said in a statement, accusing Cambodian forces of firing mortar rounds into Thailand’s Ubon Ratchathani province.

One soldier was wounded by shrapnel and being evacuated for medical treatment, it added.

The Thai army said in a later statement that the Cambodian side had contacted a Thai military unit and claimed “there was no intention to fire into Thai territory”, adding “the incident was caused by an operational error by Cambodian personnel”.

“The Thai military in the area warned Cambodian forces to exercise caution and stressed that if a similar incident were to occur again, Thailand may need to take retaliatory action,” the statement said.

Cambodia’s defence ministry spokeswoman Maly Socheata declined to comment on the alleged strike.

Thailand’s Prime Minister Anutin Charnvirakul said his government had lodged a protest with Phnom Penh, “stating that the truce was violated”.

“At the military-to-military level, we have been told the incident was an accident, but we are seeking clarification on how responsibility will be taken,” Anutin told reporters in Bangkok.

He said Thailand had the “capability to respond” to Cambodia, which is vastly outgunned by its neighbour.

Provincial governors had received orders to “make preparations, though no evacuation of residents has been ordered at this stage”, Anutin added.

Hundreds of thousands of people on both sides of the border who were displaced by the clashes in December have begun returning home since the ceasefire was agreed last month.

‘Goodwill’

The nations’ long-standing conflict stems from a dispute over the colonial-era demarcation of their 800-kilometre (500-mile) border, where both sides claim territory and centuries-old temple ruins.

Under the December truce, Cambodia and Thailand pledged to cease fire, freeze troop movements and cooperate on demining efforts along their border.

On December 31, Bangkok released 18 Cambodian soldiers held since July when deadly border clashes that month killed dozens of people.

Thailand’s foreign ministry said their release was “a demonstration of goodwill and confidence-building”.

Phnom Penh said last week it remained “hopeful” that their return would “significantly contribute to building mutual trust”.

The United States, China and Malaysia had brokered a truce to end the fighting between Cambodia and Thailand in July, but that ceasefire was short-lived.

In October, US President Donald Trump jetted to Malaysia to oversee the signing of a follow-on declaration, touting new trade deals after the neighbours agreed to prolong their truce.

But Bangkok suspended the agreement the following month, after Thai soldiers were wounded by landmines while on patrol at the border.

Disputed border

On Saturday, one week after the December truce went into effect, Cambodia called on Thailand to pull out its forces from several border areas Phnom Penh claims as its own.

The Thai military has rejected claims it had used force to seize Cambodia territory, insisting its forces were present in areas that had always belonged to Thailand.

While the two nations agreed late last month to stop fighting, they still need to resolve the demarcation of their disputed border.

Cambodia’s defence ministry said in a statement Tuesday morning that Phnom Penh had proposed a bilateral border committee meeting with Thai counterparts to be held in Cambodia’s Siem Reap province this month.

Bangkok has said previously that meetings to discuss border surveying and demarcation may need to be held by Thailand’s next government, following elections scheduled for February 8.