One Thai soldier was killed, and eight others wounded, according to Thai army spokesperson Major General Winthai Suvaree, who also said Cambodian troops fired first into Thai territory.
Thailand used aircraft "to strike military targets in several areas to suppress Cambodian supporting fire attacks," he added.
At least four Cambodian civilians have been killed and nine injured, Cambodia's information minister Neth Pheaktra said.
Cambodian officials said the Thai military attacked their troops first in Preah Vihear province.
"Cambodia urges that Thailand immediately stop all hostile activities that threaten peace and stability in the region," said Cambodian defence ministry spokesperson Maly Socheata.
Tensions have simmered since the neighbouring countries signed a US-brokered ceasefire agreement in October, put forward by President Donald Trump.
Their territorial disputes led to five days of combat in July that killed dozens of soldiers and civilians.
Thai Prime Minister Anutin Charnvirakul said that military operations would be carried out as necessary to defend the country and protect public safety.
"Thailand has never wished for violence. I'd like to reiterate that Thailand has never initiated a fight or an invasion, but will never tolerate a violation of its sovereignty," he said.
In Thailand, more than 385,000 civilians across several border districts are being evacuated, with over 35,000 already housed in temporary shelters, military officials said.
Meanwhile, the Cambodian Education Ministry said several schools along the border had been shut.
Footage posted online showed what appeared to be students hurriedly leaving classes to meet their parents.
Malaysia's Prime Minister Anwar Ibrahim urged Thailand and Cambodia to "exercise maximum restraint".
In a post on social media, he added: "Our region cannot afford to see long-standing disputes slip into cycles of confrontation."
Si Sa Ket, Surin and Ubon Ratchathani provinces in Thailand, and Cambodia's Preah Vihear and Oddar Meanchey provinces were among the areas said to be caught up in the latest clashes.
On Sunday, both nations accused each other of opening fire along the border in what the Thai army said was an incident that lasted around 20 minutes and resulted in the injury of two of its soldiers.
But Cambodia said that the Thai side fired first and that Cambodian troops did not retaliate.
Read more:
Thailand-Cambodia peace deal in trouble
Cambodian soldiers returned by Thailand
For more than a century, Thailand and Cambodia have contested sovereignty at points along their 508-mile (817km) land border.
Prince Harry wrote to Home Secretary Shabana Mahmood shortly after her appointment and submitted a formal request for a risk assessment to the Executive Committee for the Protection of Royalty and Public Figures (Ravec), a source close to the duke told the PA news agency in October.
Now the Home Office, which oversees Ravec, has ordered a threat assessment for the first time since 2020, according to The Sun.
In May, the duke lost an appeal challenging the dismissal of his High Court claim against the Home Office over the decision of Ravec to downgrade his level of taxpayer-funded protection when he is back in the country.
Ravec made its decision in February 2020 after Harry and Meghan stopped working as senior royals, and went to live in Canada and then later the US.
The duke said the Court of Appeal decision meant it is now "impossible" for him to bring his wife and their children, Prince Archie and Princess Lilibet, back to the UK safely.
Ravec has now instructed its Risk Management Board to reassess his threat level, according to The Sun.
The newspaper said the process is already underway, and a decision is expected next month.
Read more:
Prince Harry apologises to Canada for wearing cap
What you need to know about Harry's case against publisher
A government spokesperson said: "The UK government's protective security system is rigorous and proportionate.
"It is our long-standing policy not to provide detailed information on those arrangements, as doing so could compromise their integrity and affect individuals' security."
It comes after The Daily Telegraph reported that during Harry's last visit to the UK in September, a "known stalker" came "within feet" of him on two occasions.
Tadhg Farrell and 60-year-old Mary Holt died following the blaze at a house in Castleview Park in Edenderry, County Offaly, at around 7.45pm on Saturday.
Another woman in her 50s is being treated in hospital for her injuries.
Superintendent Liam Geraghty confirmed a murder investigation had been launched during a news conference at Edenderry Garda Station on Sunday.
He said they believe that the house was attacked by a person or persons unknown at this time and that the fire was deliberately started.
He described a "reckless, callous and murderous attack on a family home".
Irish minister for justice Jim O'Callaghan strongly condemned what he described as a "deliberate callous attack" on the house.
Gardai in Tullamore are appealing for witnesses to come forward.
A yellow weather warning for rain comes into effect from 6pm on Monday, and will be in place for 24 hours, covering parts of southwest England and Wales, and stretching to parts of Herefordshire and Hampshire.
The Met Office has also issued a yellow warning for high winds from Dorset to Cornwall and up to north Wales, in place from 10pm on Monday until 4pm on Tuesday.
It said transport networks could face disruption, with delays for high-sided vehicles on exposed routes and bridges, and coastal roads and seafronts affected by spray and large waves. Power outages are also possible.
For 24 hours from 6pm on Monday, up to 40mm of rain could fall in some areas, with 60-80mm of rain over Dartmoor and high ground in South Wales, which would amount to more than half the average monthly rainfall in December.
Check the weather forecast where you are
The predicted rainfall across southwest England and South Wales is expected to hit already saturated ground and could lead to difficult travel conditions.
Another rain warning is in place for northwest England from midnight on Tuesday until 3pm, while a wind warning has been issued for northwest Scotland from 3pm on Tuesday until 10am on Wednesday.
The Met Office's deputy chief meteorologist, Steven Keates, said: "A deepening area of low pressure will approach the UK from the southwest later on Monday, bringing with it heavy rain and strong winds, which are likely to affect the UK between late Monday and early Wednesday.
"The exact track, depth and timings of this low are uncertain, which makes it harder to determine where will be most impacted by strong winds and/or heavy rain.
"This system has the potential to cause disruption, and severe weather warnings are likely to be issued over the weekend as details become clearer. We therefore urge people to keep up-to-date with the latest Met Office forecast."
The Met Office said the rest of the month remained unsettled, with further periods of low pressure predicted.
It also said it is too early to provide an accurate forecast for the Christmas period.
Henry Nowak, 18, of Chafford Hundred, Essex, suffered a puncture wound to his chest and two to the back of his leg during an incident in Belmont Road, Portswood, Southampton, on Wednesday. He died at the scene.
In a statement, his family said he was "fully embracing university life" and was "loved by all those that knew him", adding he had been on a night out with his "new football teammates" when he died.
Vickrum Digwa, of St Denys Road, Southampton, has been charged with murder, Hampshire Constabulary said.
The suspect has also been charged with possession of a bladed article in a public place.
Kiran Kaur, 52, of St Denys Road, Southampton, has been charged with assisting an offender.
Both are due to appear at Southampton Magistrates' Court on Monday.
A 51-year-old man, previously arrested on suspicion of murder, has been released on police bail pending further enquiries.
And a 26-year-old man, who had been arrested on suspicion of murder, has been released with no further action in relation to that offence but was additionally arrested on suspicion of assisting an offender and a public order offence.
He has been released on police bail pending further enquiries.
Read more from Sky News:
Reform UK denies Nigel Farage broke electoral law
Hundreds of books at the Louvre damaged in water leak
Paying tribute to Mr Nowak, his family said in a statement, released through police, that he was an "all-round top lad", adding: "Our kind, intelligent and talented son was in his first year at Southampton University studying accountancy and finance.
"He'd smashed his A-levels and was fully embracing university life, joining not one but two football teams, making new friends as well as working part-time at the local Morrisons.
"Henry was loved by all those that knew him. He was an incredible son, brother, cousin, grandson, nephew, friend and teammate.
"He went on a night out with his new football teammates, celebrating the end of their first semester at uni. Devastatingly, he never made it home.
"Our hearts ache when we think of the bright future he had ahead of him, full of opportunity and adventures.
"There are no words to describe just how heartbroken we are that we will never get to see him grow and fulfil his awesome potential.
"We are so proud of him and all he achieved.
"Our world will never be the same without our amazing Henry."




