The escalation of military exchanges between Thailand and Cambodia could move towards war, Acting Thai Prime Minister Phumtham Wechayachai has said.
"If the situation escalates it could develop into war, though for now it remains limited to clashes."
Thai and Cambodian soldiers are continuing to clash along the border between their countries in a major escalation that has so far left at least 16 people dead, mostly Thai civilians.
The two sides fired small arms, artillery and rockets, and Thailand also launched air strikes in the bloodiest military battles in more than a decade between the two South-East Asian neighbours.
Thailand has rejected mediation efforts from third countries to end the ongoing conflict with Cambodia, insisting that Phnom Penh cease attacks and resolve the situation only through bilateral talks, its foreign ministry said on Friday.
The United States, China and Malaysia, which is the current chair of the ASEAN regional bloc, have offered to facilitate dialogue but Bangkok is seeking a bilateral solution to the conflict, Thai foreign ministry spokesperson Nikorndej Balankura told Reuters.
"I don't think we need any mediation from a third country yet."
The conflict presented a predicament for South-East Asia, a leading expert says, with questions remaining over how the two countries and the region will respond.
Landmine triggers escalation
Clashes between Thailand and Cambodia have taken place in 12 locations along their disputed border, up from six on Thursday, a Thai military official said.
Rear Admiral Surasant Kongsiri, a military spokesperson, told a press conference, Cambodia had continued to use heavy weapons.
The conflict erupted after a landmine detonated and wounded five Thai soldiers on Wednesday in an area that Thai authorities said should have been safe.
The incident led Bangkok to withdraw its ambassador from Cambodia and expel Cambodia's envoy to Thailand.
On Thursday, Cambodia fired rockets and artillery shells into Thailand and the Thai military scrambled F-16 jets to carry out air strikes.
In Bangkok, the Public Health Ministry said a Thai soldier and 14 civilians, including children, were killed, while 46 people, including 15 soldiers, were injured.
Most of the causalities were caused by a rocket strike near a petrol station in Sisaket province.
Public Health Minister Somsak Thepsuthin condemned what he said were the attacks on civilians and a hospital as violations of international humanitarian law and the Geneva Conventions.
"We urge the Cambodian government to immediately halt these war criminal actions, and return to respecting the principles of peaceful coexistence," he said.
[MAP]On Friday, Cambodia's chief official in Oddar Meanchey province, General Khov Ly, said clashes resumed early in the morning near the ancient Ta Muen Thom temple.
A spokesperson for the province's administration said a 70-year-old man was killed and five were wounded, with 1,500 families evacuated.
The escalation represents a rare instance of military conflict between member countries of the Association of South-East Asian Nations (ASEAN), though Thailand has tangled with Cambodia before over the border and has had sporadic skirmishes with western neighbour Myanmar.
UN Secretary-General Antonio Guterres urged both sides "to exercise maximum restraint and address any issues through dialogue", according to UN deputy spokesperson Farhan Haq.
Thailand and Cambodia have blamed each other for the clashes, alleging that civilians were being targeted.
The fighting is the latest chapter in a long-running spat over an area known as the Emerald Triangle, where the borders of both countries and Laos meet.
The decades-old squabble flared into bloody clashes more than 15 years ago and again in May, when a Cambodian soldier was killed in a firefight.
Praphas Intaracheun, a 53-year-old gardener from Sisaket, told AFP that he was refuelling at another petrol station about 300 metres from the one that was hit on Thursday.
"I heard a loud noise three or four times, and when I looked over, there was a gigantic cloud of smoke," he said.
A 30-bed hospital in the town of Phanom Dong Rak in Surin province, just 15 kilometres from the border, was hit by shells which shattered windows and collapsed part of a roof.
The facility was partially evacuated on Wednesday night as a precaution.
Locals flee border zones
Fighting was focused on six locations, the Thai army said, with ground troops and tanks battling Cambodian forces for control of territory.
More than 138,000 people and 428 hospital patients from border provinces were evacuated or moved to nearly 300 temporary shelters, the Thai health ministry said.
Six Thai air force jets were deployed, hitting two "Cambodian military targets on the ground", according to Thai military deputy spokesperson Ritcha Suksuwanon.
AFP journalists met Cambodians fleeing their villages near the Thai border to escape the fighting.
"We dare not to stay. They were fighting so bad that my house was shaking," Say Vuthy said.
"We already dug a bunker but we dared not stay because we were scared that they will keep fighting at night."
In Cambodia, several hundred villagers moved from their homes near the border to about 30 kilometres deeper inside Oddar Meanchey province.
Director of the Asia-Pacific program at policy think tank Chatham House, Ben Bland, said that domestic politics and public opinion were key driving factors in the conflict.
"We know that a lot of temples that are on the border are really important, symbolically and culturally, for people in Cambodia," Mr Bland said.
He said Cambodia was invaded in the past and went through decades of conflict, while Thailand, a "proud country", was amid a "very messy" domestic political situation.
"This has been driven by politics and sustained by … some nationalist opinion in both countries."
Thai Foreign Ministry spokesperson Nikorndej Balankura said the government was "prepared to intensify our self-defence measures if Cambodia persists in its armed aggression and violations upon Thailand's sovereignty".
Cambodian Defence Ministry spokesperson Lieutenant General Maly Socheata said his country deployed armed force because "it has no choice but to defend its territory against Thai threats".
The spokesperson insisted the Cambodian "attacks are focused on the military places, not on any other place".
Cambodian Prime Minister Hun Manet wrote to the UN Security Council asking for an urgent meeting "to stop Thailand's aggression".
The council scheduled an emergency closed meeting at 3pm in New York on Friday.
Mr Bland said the violence was "really concerning" but both countries had shown the ability to de-escalate tensions in the past.
"There's more of a risk that it becomes a protracted diplomatic and economic battle between the two, and I think that would potentially have knock-on effects economically," Mr Bland said.
"It just creates another point of tension for South-East Asian nations when they're already facing the impacts of the civil war in Myanmar, US-China tensions and Trump's tariffs.
Foreign Minister Penny Wong said Australia was "deeply concerned" by escalating tensions across the Thai-Cambodian border, including reports of injuries and loss of life.
"We urge both sides to de-escalate and resolve border issues peacefully," she said in a post on X.
Malaysia's prime minister said he spoke to both leaders and the United States, European Union, France and China, a close ally of Phnom Penh, all called for peace.
The Australian government has urged travellers to reconsider the need to travel to border areas in both Cambodia and Thailand because of the conflict.
ABC/Wires
