PHNOM PENH, July 31, 2025 (BSS/AFP) - Cambodia called on Thailand Thursday to return 20 soldiers it said were taken captive hours after a ceasefire to halt the neighbours' bloodiest border clashes in decades.

The two countries agreed a truce on Tuesday following five days of clashes that killed at least 43 people on both sides -- the latest eruption of a long-standing dispute over contested border temples on their 800-kilometre (500-mile) frontier.

Bangkok said there were no reports of violence during the night up to 7:00 am (0000 GMT), after both sides traded allegations of ceasefire breaches on Wednesday.

Cambodian defence ministry spokeswoman Maly Socheata said Thursday that talks were under way for the release of 20 soldiers.

"We will do our best to continue negotiations with the Thai side in order to bring all our soldiers back home safely and as soon possible," she told a briefing.

"We call on the Thai side to send all 20 military personnel back to Cambodia as soon possible."

The troops were captured around 7:50 am on Tuesday, she said -- nearly eight hours after the ceasefire came into effect.

Thailand's government said Wednesday the detained soldiers were being treated in line with international humanitarian law and military regulations, and would be returned when the border situation stabilises.

UN rights chief Volker Turk urged the neighbouring nations to implement their ceasefire deal in full and take rapid steps to build confidence and peace.

"This crucial agreement must be fully respected, in good faith, by both sides, as diplomatic efforts continue, in a bid to resolve the root causes of the conflict," he said.

The agreement to stop fighting was sealed in Malaysia after an intervention by US President Donald Trump -- who both Thailand and Cambodia are courting for a trade deal to avert his threat of eye-watering tariffs.

Nearly 300,000 people fled their homes as the two sides battled with jets, rockets and artillery along the rural border region, marked by a ridge of hills surrounded by wild jungle and agricultural land where locals farm rubber and rice.

Thailand has said 15 of its soldiers and 15 civilians were killed, while Cambodia has confirmed eight civilian and five military deaths.

The death toll is significantly higher than in the last major flare-up of violence on the border, when 28 were killed in sporadic fighting from 2008 to 2011.