New cross-border fighting has killed at least five people, with both countries accusing each other of provoking the violence.
The latest flare-up comes despite a recent ceasefire agreement, with tensions escalating since May and over 40 deaths reported.
Thailand and Cambodia continue to dispute sovereignty along their 800km border, a conflict rooted in century-old territorial claims.
Residents on both sides of the Thailand–Cambodia border evacuated en masse on Monday as renewed clashes erupted, leaving at least five people dead.
Each country has accused the other of triggering the violence, marking the most serious confrontation since a ceasefire was agreed in July.
Thailand’s Prime Minister Anutin Charnvirakul said his country "never wanted violence" but would "use necessary means to preserve its sovereignty", while Cambodia’s former leader Hun Sen accused Thai "invaders" of provoking retaliation.
Since May, rising tensions between the neighbours have resulted in more than 40 deaths, alongside import bans and travel restrictions. On Monday, the Thai army said its troops responded to Cambodian fire in Thailand’s Ubon Ratchathani Province, including launching air strikes along the disputed border; meanwhile, Phnom Penh’s defence ministry said Thai forces initiated the assault in Cambodia’s Preah Vihear province.
Officials on both sides said at least one Thai soldier and four Cambodian civilians had been killed, with around a dozen more wounded in Monday’s fighting.
Nearly 650 schools across five Thai provinces have been ordered to close for safety reasons, the education minister said, following fresh tensions that have simmered since Sunday.
Videos shared on social media show chaotic scenes in schools across Cambodia’s border provinces as parents rushed to collect their children.
In July, in the middle of exams, five days of heavy fighting broke out between the two countries.
Afterwards, Pongsuwan’s school moved to online classes, but many students could not access them due to a lack of internet at home, while school-issued iPads did not reach everyone.
In Cambodia, former journalist Mech Dara posted several clips on his X account showing children running from their schools.
"How many times [do these] kids have to suffer the shocking environment?" he wrote. "The nonsense fighting bring kids [a] horrible nightmare."
He also posted an image of a boy in his school uniform eating in an underground bunker. "Why does the kid and his family have to eat their meal in the bunker...?" he wrote.
Meanwhile, Pongsuwan told the BBC that he and his neighbours remain unsure whether to evacuate, even as gunfire intermittently echoes through their village.
"If you ask whether we're scared, yes we are... Should we leave? Will it really be safer? Or should we stay?" he told the BBC.
The century-old border dispute dramatically escalated on 24 July when a Cambodian rocket barrage struck Thailand, followed by Thai air strikes.
Days later, Bangkok and Phnom Penh agreed to an "immediate and unconditional ceasefire" brokered by Malaysian Prime Minister Anwar Ibrahim.
In October, both sides signed a ceasefire agreement in Malaysia during a ceremony attended by US President Donald Trump, who hailed it as a historic achievement in resolving the conflict.
But two weeks later, Thailand said it would suspend implementation of the deal after two of its soldiers were injured by a landmine near the Cambodian border.
Cambodia, which nominated Trump for a Nobel Peace Prize for his role in brokering the ceasefire, has insistently maintained that it remains committed to the agreement.
Thailand and Cambodia have contested sovereignty along their 800km border for more than a century, dating back to its demarcation following French colonial rule in Cambodia.
(with inputs from BBC )
