SURIN, Thailand — Cambodia's powerful Senate President Hun Sen on Tuesday vowed a fierce fight against Thailand as a second day of widespread renewed combat between the Southeast Asian neighbors drove tens of thousands of people to flee border areas.

Fighting broke out following a skirmish on Sunday during which two Thai soldiers were injured, derailing a ceasefire that ended fighting over competing territorial claims in July. The five days of fighting then left dozens dead on both sides, and forced the evacuation of over 100,000 civilians.

Both sides vow to keep fighting

In a sign that neither side was willing to back down, Thai Prime Minister Anutin Charnvirakul said Tuesday that Cambodia had not yet contacted Thailand about possible negotiations and the fighting would continue.

“We’ve got to do what we’ve got to do,” he said. “The government will support all kinds of military operations as planned earlier.” He said Monday that military action was necessary to safeguard the nation’s sovereignty and ensure public safety.

In a statement posted to Facebook and Telegram, Hun Sen claimed that his country had refrained from retaliating on Monday, but overnight began to fire back at Thai forces.

"Cambodia wants peace, but Cambodia is forced to fight back to defend its territory," Hun Sen wrote. He was Cambodia's long-serving prime minister until 2023, when he was succeeded by his son Hun Manet, but is still widely seen as the country's de facto leader.

Thailand’s military said Cambodia attacked Thai positions with artillery and rocket and drone attacks on Tuesday. Thailand said that Cambodian forces also fired at its troops Sunday and Monday, but each side blames the other for shooting first.

Cambodia’s military announced Tuesday that the new fighting had killed seven civilians and wounded 20. A Thai military spokesperson said that three soldiers have been killed.

Thailand on Monday carried out airstrikes along the frontier, which it called a defensive action targeting military installations. Thai military spokesperson Rear Adm. Surasant Kongsiri said Tuesday that such operations would continue “until attacks stop.”

Villagers on both sides flee to safety

An evacuation shelter at a university in Thailand's northeastern city of Surin hosted more than 3,600 people who were relocated from the danger zones. They sat or laid on thin mats and several set up small tents. At lunchtime, some lined up to receive cooked rice, while others were served ready-to-eat meals. An army band played for their entertainment.

“We were preparing to evacuate. We hadn’t left yet. But when we heard shots we hurried out immediately," cassava farmer Pan-ngam Kanchangthong told The Associated Press. "I was scared. Who wouldn’t be scared of shelling?”

The Thai army said almost 500 temporary shelters were set up in four border provinces, accommodating 125,838 people.

Evacuees on the Cambodian side had similar experiences.

“I felt terrified when I heard the sound of the explosion from the shelling. At that time, I was working at the garment factory," said 44-year-old Vach Neang, a father of seven.

“I called my wife and my kids but couldn't reach them, and by that time the sound of explosions was getting louder, so the factory owner let us go home," he said, speaking at a former market in Cambodia’s northwestern province of Banteay Meanchey that has been repurposed as a shelter. He added that he packed just a few clothes before fleeing.

Cambodian Information Minister Neth Pheaktra said almost 55,000 people have been evacuated and the numbers were mounting.

The two nations have a history of ill will

Thailand and Cambodia have a history of enmity over centuries and experience periodic tensions along their land border of more than 800 kilometers (500 miles). Centuries ago both were powerful empires, but Thailand's size and greater development over the past century give it the military advantage.

Some of the disputed territory hosts ancient temples that both nations covet as part of their heritage. Cambodia's Culture Ministry charged that Thai forces on Tuesday had damaged one, Ta Krabey temple, calling the alleged action “a reprehensible act (reflecting) profound immorality.”

Thailand's military, referring to the same 11th-century temple by its Thai name, alleged that Cambodian forces launched rocket attacks into the northeastern province of Surin. Independent corroboration of either claim was impossible.

The ceasefire that ended July’s fighting was brokered by Malaysia and pushed through by pressure from U.S. President Donald Trump, who threatened to withhold trade privileges from the two nations unless they agreed to it.

In Washington, U.S. Secretary of State Marco Rubio said in a statement that the United States is concerned by the uptick in violence and called for both sides to live up to the commitments they made in Kuala Lumpur in late October.

“We strongly urge the immediate cessation of hostilities, the protection of civilians, and for both sides to return to the de-escalatory measures outlined in the October 26 Kuala Lumpur Peace Accords signed by the Prime Ministers of Cambodia and Thailand and witnessed by President Trump and Malaysian Prime Minister Anwar Ibrahim,” Rubio said.

The agreement called for removing heavy weapons from the border, desisting from disseminating false information and harmful rhetoric, implementing measures to restore mutual trust and coordinating operations to remove land mines.

None of these actions appear to have been fully implemented by either side. After the ceasefire, both nations continued to fight a bitter propaganda war using disinformation, alongside minor outbreaks of cross-border violence.

Prisoners and land mines have been sticky issues

A major Cambodian complaint has been that Thailand continues to hold 18 prisoners who were taken the same day the ceasefire went into effect. Thailand claims they approached its positions in a threatening manner, an allegation denied by Phnom Penh.

Thailand accuses Cambodia of laying new land mines in the areas under dispute, in several cases maiming Thai soldiers. Cambodia says the mines are left over from decades of civil war that ended in 1999.

The mines issue caused Thailand to declare earlier this month that it was indefinitely pausing implementation of the details of the ceasefire until Cambodia apologized for wounding Thai soldiers.

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A previous version of this story incorrectly reported that a Thai soldier was killed during a skirmish on Sunday. Two Thai soldiers were injured during the skirmish on Sunday, according to the Thai military, but none were reported killed.

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Sopheng Cheang reported from Mongkol Borey, Cambodia. Associated Press writers Wasamon Audjarint in Bangkok and Matthew Lee in Washington contributed to this report.

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