At least a dozen people were killed after the two countries exchanged fire after simmering tensions over a border dispute boiled over on Thursday.

Armed clashes have broken out between Thailand and Cambodia in long-disputed border areas, rapidly escalating months-long tensions.

Thailand and Cambodia exchanged fire along their disputed border for a second day on Friday, officials from both countries said, with more than a dozen people reported killed and more than 135,000 civilians evacuated.

The Pheu Thai Party has dismissed allegations that the Thai-Cambodia border dispute stems from personal or political rivalries between the Shinawatra and Hun Sen families, instead attributing it to Phnom Penh’s dissatisfaction with Thailand’s aggressive crackdown on Cambodia-based online scam centres.

Thailand claims the ordnance was newly laid, but Cambodia says they are leftovers from a final stint of fighting during the murderous Khmer Rouge regime. Still, soon after the incident, both sides downgraded relations, expelled their neighbour’s ambassador and recalled embassy staff.

Thailand and Cambodia exchanged heavy artillery fire for a second day on Friday as border fighting intensified and spread, while Cambodia's leader said Thailand had agreed to a Malaysian ceasefire proposal but then backed down.