Around 35,000 people in Thailand have been evacuated from border areas, the country's Second Army Region said.

Five days of combat this summer between the two Southeast Asian nations killed 43 people and displaced around 300,000 on both sides of the border before a truce took effect.

But last month Thailand paused a follow-on deal backed by US President Donald Trump to wind down hostilities, saying a landmine blast at the border had wounded several soldiers.

Cambodian and Thai officials have since reported sporadic skirmishes along their frontier, which reignited Sunday and Monday.

Cambodia's information minister Neth Pheaktra told AFP that at least four Cambodian civilians were killed by Thai shelling Monday in the border provinces of Preah Vihear and Oddar Meanchey.

Around 10 other civilians were wounded, including a Cambodian journalist who was hit by shrapnel from a Thai rocket, Neth Pheaktra said.

The Thai army said one soldier was killed and 18 others were wounded since fresh fighting began Sunday.

The European Union called on the two countries Monday to "exercise maximum restraint" and dial down hostilities, remarks echoed by the United Nations.

UN Secretary-General Antonio Guterres urged both parties "to avoid further escalation" and "recommit to the ceasefire" brokered earlier this year, his spokesman said.

Washington, through its embassy in Bangkok, urged Americans to avoid all travel within 50 kilometres (31 miles) of the Thai-Cambodia border "due to active hostilities and the unpredictable security situation."

Farmer Pannarat Woratham, who lives a few kilometres from the border in Thailand's Surin province, said she fled Sunday afternoon to a temple sheltering the displaced.

It was the second time the 59-year-old had evacuated since late July when open combat was waged with fighter jets, missile strikes and ground troops, killing both civilians and soldiers.

"Of course many of us thought the conflict was finally over. It shouldn't have happened again like this," Pannarat told AFP.

Across the border, Cambodian Hul Malis said the Thai military entered the border village of Prey Chan on Monday afternoon just 20 minutes after she fled.

"They came in with tanks," Hul Malis said other residents told her.

"I am so scared and I am running away."

Prey Chan was the site of a stand-off in September between several hundred Cambodian demonstrators and Thai forces who fired rubber bullets and tear gas at them. Both countries claim the area as their own territory.

Neth Pheaktra, the minister, told reporters that at least 1,157 families had evacuated to safety in Oddar Meanchey alone.

The conflict centres on a century-old disagreement over borders mapped during France's colonial rule in the region, with both sides claiming a smattering of boundary temples.

- 'Military objectives' -

Both sides reported a brief Sunday skirmish, which Thailand's military had said left two soldiers wounded.

But the fighting escalated early Monday.

Thai army spokesman Winthai Suvaree said it had launched air strikes against Cambodia in self-defence.

"The Thai air power is being used only against Cambodian military targets" and has had "no impact on civilians," Winthai told reporters.

But Cambodia's defence ministry spokeswoman Maly Socheata said Thai forces had attacked Cambodian troops in Preah Vihear and Oddar Meanchey early Monday, and accused Thailand of "firing multiple shots with tanks" near centuries-old temples.

Maly Socheata later told reporters the Thai military attacked Cambodian forces in Preah Vihear with an F-16 jet.

She said Thailand's military had not ceased their attack and expanded the battle. She maintained Cambodia had not retaliated.

The Thai army, meanwhile, has accused Cambodian forces of firing BM-21 rockets towards civilian areas in Buriram province, with no casualties reported.

- 'Cycles of confrontation' -

The United States, China and Malaysia, as chair of the regional bloc ASEAN, brokered the cessation of fighting in July.

In October, Trump co-signed a follow-on joint declaration, touting new trade deals with Thailand and Cambodia after they agreed to prolong their ceasefire.

But Thailand suspended the agreement the following month, and the two sides then traded accusations of renewed clashes.

Asked about Trump's intervention and a call by Malaysian Prime Minister Anwar Ibrahim for restraint and diplomacy, Thai Prime Minister Anutin Charnvirakul told reporters in Bangkok that no one should tell his country to stop.

"We're long past that point," he said. "If you want things to stop, tell the aggressor to stop."

burs-sco/mlm/iv