Fighting between Thailand and Cambodia spread Tuesday to new parts of their contested border as the toll rose to 10 killed and more than 140,000 civilians fled the violence.
The two countries have blamed each other for the renewed clashes over their century-old border dispute, which saw Thailand launch air strikes and use tanks against its neighbour on Monday.
Cambodia's influential former leader Hun Sen said his country had retaliated against Thailand, after Phnom Penh denied firing back for two days.
This week's clashes are the most deadly since the neighbouring nations engaged in five days of intense combat in July that killed dozens of people and displaced around 300,000 before a truce took effect.
Tens of thousands of people have evacuated from border regions since the fresh fighting began on Sunday, officials said.
Cambodian Poan Hay, 55, said she left her home in Oddar Meanchey province on Monday as soon as she heard gunfire -- the fourth time she evacuated this year due to on-and-off fighting on the frontier.
"I am so angry at the Thai army, but I ask them to stop firing at Cambodians," Poan Hay told AFP.
She is sheltering at a pagoda with relatives about 70 kilometres (43 miles) from the border in Siem Reap province's Srei Snam.
"For the last five months, I couldn't sleep a lot. I was worried about our safety," she said.
"Yesterday Thai jets flew along the border. I was so scared."
Phnom Penh accused Thai forces of shelling positions overnight, which killed two people travelling on a national road.
Seven Cambodian civilians have been killed in total and about 20 wounded this week, Cambodia's interior ministry said in a statement.
More than 21,000 people have been displaced from three border provinces, the ministry added.
The defence ministry said the Thai army had resumed attacks around 5:00 am Tuesday in border regions, including in the area of centuries-old temples, such as the UNESCO world heritage site, the Preah Vihear temple.
The Thai army said three soldiers have been killed since Monday.
One was killed Tuesday by indirect fire in Surin province while a grenade killed another soldier in the area of the Preah Vihear temple.
Nearly 500 temporary shelters have been established across several border provinces, housing more than 125,000 civilian evacuees, according to a government statement.
Thai navy spokesperson Parat Rattanachaiphan said in a press conference that Thai forces recently detected Cambodian troops, settlements and several weapon bases in a disputed coastal area of Trat province.
Parat accused Cambodia of escalating tensions by deploying unmanned drones to provoke Thai forces.
Early Tuesday, he said Thai forces "launched a military operation to drive them out".
- Century-old dispute -
Cambodia's Senate president and former prime minister, Hun Sen, said Tuesday his country had retaliated after remaining "patient for more than 24 hours in order to respect the ceasefire and for time to evacuate people to safety".
"Now we fight in order to defend ourselves again," he said in a Facebook post.
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.
Thai Prime Minister Anutin Charnvirakul told reporters his country's military would remain resolute.
"Thailand must stand firmly behind those who protect our sovereignty. We cannot stop now," he said.
In Thailand's Surin province, Sutida Pusa, 30, who runs a small food shop, told AFP on Monday that her young and elderly relatives were moved to an evacuation centre the day before, while others stayed behind to guard their property.
She has travelled back and forth between the temporary shelter and her house -- located less than 20 kilometres from the border -- to care for family members in both places.
"I wanted to see the situation first, as the sounds of fighting aren't as loud as during the major clash on July 24," she said.
"We never trust the situation."
The Thai army said Tuesday that Cambodian shells had fallen on two civilian homes in Sa Kaeo province, with no casualties reported.
The United States, China and Malaysia, as chair of the regional bloc ASEAN, brokered the cessation of fighting in July.
In October, US President Donald Trump backed 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 fresh clashes.
UN Secretary-General Antonio Guterres, the European Union and Malaysia's prime minister on Monday urged both parties to exercise restraint and halt hostilities.
