Fighting has reignited between Thailand and Cambodia in multiple areas at their disputed border, with both sides blaming the other and Thailand carrying out air strikes on what it said were Cambodian military installations.
The latest flare-up will be a major test of a ceasefire brokered by US President Donald Trump in July.
Conflict erupted before dawn on Monday, with clashes in five border locations, according to Thailand's army.
Each side blamed the other for starting clashes that broke out during the night and intensified before dawn and spread to several locations, with one Thai soldier and four Cambodian civilians killed, according to officials.
Cambodia accused Thailand of "inhumane and brutal acts" of aggression, stressing it had not retaliated, while Bangkok said it carried out air strikes on military targets after its neighbour mobilised heavy weaponry and repositioned combat units.
The Thai air force said its fighter jets launched air strikes early in the morning, targeting military installations, based on operational assessments that showed Cambodia had mobilised heavy weaponry and re-positioned combat units.
Thailand said 380,000 people were being moved to shelters and Cambodian authorities said 1,157 families were being relocated from Oddar Meanchey province.
What led up to the fighting?
The renewed fighting is the most serious since a five-day exchange of rockets and heavy artillery in July that marked their worst fighting in recent history. At least 48 people were killed and 300,000 displaced before Trump intervened to bring about a truce.
It is not immediately clear what sparked the latest unrest, but tensions have simmered since a Thai soldier was wounded by a landmine on 10 November, prompting Thailand to suspend de-escalation measures agreed in an enhanced ceasefire deal a few weeks earlier in Malaysia in Trump's presence.
Thailand says the landmine was among several that were newly laid by Cambodia and that it would not resume the de-escalation measures until Cambodia apologises. Cambodia has repeatedly rejected the allegations.
US President Donald Trump (right) brokered a peace deal signed by Thailand's Prime Minister Anutin Charnvirakul (centre) and Cambodia's Prime Minister Hun Manet (left) in October. Source: AP / Mohd Rasfan
How do the two countries compare militarily?
Thailand has a large and well-funded military that dwarfs that of Cambodia, with triple the active armed forces personnel and a 2024 defence budget allocation that was four times bigger than its neighbour's.
Cambodia's military budget is a quarter the size of Thailand's. Source: EPA / Kith Serey
Thailand's air force has nearly 40 fighter jets and dozens of helicopters, while Cambodia has 16 multi-role helicopters but no fighter aircraft.
Where does the dispute originate?
Thailand and Cambodia have for more than a century contested sovereignty at various undemarcated points along their 817km land border, which was first mapped by France in 1907 when Cambodia was its colony.
That map, which Thailand later contested, was based on an agreement that the border be demarcated along the natural watershed line between the two countries.
In 2000, they agreed to establish a commission to peacefully address overlapping claims, but little progress has been made.
Cambodian soldiers on guard at Preah Vihear temple near Cambodia's Thai border in July 2025. Source: AP / Mak Remissa
The 11th-century Hindu temple Preah Vihear, or Khao Phra Viharn in Thailand, has been central to the dispute, with both countries claiming historical ownership.
The International Court of Justice awarded the temple to Cambodia in 1962, but Thailand continued to lay claim to the surrounding land. Tension escalated in 2008 after Cambodia tried to list Preah Vihear as a UNESCO World Heritage site, leading to skirmishes and at least a dozen deaths, including during a week-long artillery exchange in 2011.
What's behind this year's troubles?
Nationalist sentiments were stirred in Thailand in 2024 when conservatives questioned a government plan to negotiate with Cambodia to jointly explore offshore energy resources, warning that it could risk Thailand losing island territory.
In May, a Cambodian soldier was killed by Thai forces during a brief skirmish, prompting both countries to increase troops at the border. Around the same time, Cambodia referred disputes over temples in four areas to the ICJ.
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