Political fugitive Sam Serey, long wanted by the Cambodian government for allegedly operating a “terrorist” group, was arrested in Bangkok on Wednesday for an immigration violation, with the Cambodian government submitting a formal request for his extradition on Thursday.

Serey, founder of the dissident group Khmer National Liberation Front, was detained for overstaying his visa.

He has been accused of various violent plots in Cambodia, though scant evidence has been given to support the allegations. Most recently, Prime Minister Hun Sen claimed he foiled a KNLF plot to bomb Wat Phnom and Siem Reap during Khmer New Year.

National Police’s chief, General Neth Savoeun, submitted a formal letter requesting his extradition Thursday, according to spokesman Kirth Chantharith.

“We have the arrest warrant from the court sentencing him to nine years in prison. Please, Thai government, send him back to serve his sentence,” Chantharith said.

He noted that as of Thursday evening, Thailand had not yet responded to the request.

The Thai government has recently been receptive to Cambodia’s extradition requests, including in the case of Sam Sokha, a Cambodian woman who fled the country after raising officials’ ire for shoe at a ruling party billboard. She was sent back to Cambodia to face jail time for the act despite having been recognised by the United Nations as a refugee.

A senior KNLF member based in Bangkok confirmed that Serey was arrested at a Thai immigration office while trying to renew an already expired visa. The source, who spoke on condition of anonymity, said Serey had been in Thailand since January.

He maintained that the arrest was “politically motivated” and done at the behest of the Cambodian government.

“The Hun Sen regime often slanders us, especially Sam Serey, as ‘terrorists’,” he said, insisting the KNLF operated nonviolently.

While more than 20 of Serey’s followers have been arrested over the years over purported violent plots, none have ever been found in possession of weapons. Serey, who received political asylum in Denmark, was sentenced in absentia to nine years in prison in 2016 for allegedly “plotting” an attack.

While evidence substantiating the terrorism charges has not been presented either publicly or in court, Serey has never satisfactorily explained the existence of photographs depicting him in non-Cambodian military gear, and posing with weapons in front of an altered Cambodian flag.

Serey’s colleague said if Thailand were to deport him to Cambodia, it would be a “serious violation of treaties and international law on political refugees”.

On Wednesday evening, the KNLF appealed to UN representatives in Bangkok, as well as the Danish Embassy. “We just received information that the embassy are intervening to help him now,” the source said on Thursday afternoon.

When reached for comment, the Danish Ministry of Foreign Affairs would only confirm that “a foreign citizen with permanent residence in Denmark is detained in Thailand”.

“In individual cases, client confidentiality applies and therefore, we cannot provide further information,” the ministry said.

Serey has vehemently denied ever planning to use violence to achieve his aims. Earlier this month, he claimed to have illegally crossed into Cambodia, but confirmed to The Post on Tuesday that he was in Thailand.

Following the extradition of Sokha, the Thai and Cambodian governments recently agreed to cooperate more fully on returning political fugitives, raising fears for the safety of numerous opposition and civil society figures currently seeking refuge in Thailand.

“Cambodia’s demands for the extradition of Serey Sam should be refused outright by Thailand. Nothing has changed the fact that he is a refugee who correctly fears political persecution if he’s returned to Phnom Penh,” said Phil Robertson, deputy director of Human Rights Watch’s Asia division via email on Thursday.

Claiming Thailand doesn’t need “another black mark on its increasingly shoddy record in protecting refugees”, he called for Serey to be deported to Denmark instead.

He also dismissed the Cambodian government’s evidence against Serey as “a joke, and a pretty bad one at that”.

The Thai Ministry of Foreign Affairs did not respond to requests for comment.