A United Nations expert group is calling for the immediate release of a Cambodian-American human rights activist, saying an investigation it conducted has concluded she was being "arbitrarily detained in violation of international law."

The United Nations Working Group on Arbitrary Detention said in a judgment late Wednesday that while attorney Theary Seng had been convicted of conspiracy to commit treason and other charges last year, she was in reality being punished for "making two posts on Facebook critical of Hun Sen," Cambodia's autocratic prime minister.

The judgment comes a little more than a week before Cambodia's general election, in which Hun Sen, who has been in power for 38 years, and his ruling Cambodian People’s Party are virtually guaranteed a landslide victory, since the Candlelight Party, the only other contender capable of mounting a credible challenge, was barred on a technicality from contesting the polls by the National Election Committee.

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The situation is similar to that of the 2018 general election, when the popular Cambodian National Rescue Party was dissolved months before the polls by a controversial court ruling that alleged it had plotted the illegal overthrow of the government.

Cambodian courts are widely believed to be under Hun Sen's influence, and pro-democracy groups have regularly criticized his government for stifling any opposition.

Theary Seng

Theary Seng, right, a Cambodian American lawyer, greets her supporters in Cambodia on Jan. 4, 2022. The United Nations Working Group on Arbitrary Detention is calling for the release of Seng who was convicted of conspiracy to commit treason. (AP Photo/Heng Sinith, File)

Theary Seng was sentenced to six years in prison last June in a trial with dozens of members of the Cambodian National Rescue Party over a failed attempt by the party's leader to return from exile in 2019.

Cambodian authorities blocked Sam Rainsy’s return and alleged that the 60 defendants were involved in organizing his trip, which Theary Seng and the others denied.

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Theary Seng escaped Cambodia as a child after her two parents were killed in the radical-communist Khmer Rouge genocide, and grew up in Michigan. She returned to Cambodia in 2004 to found two NGOs focusing on human rights and civic engagement.

Her case was submitted for a judgment to the UN working group by the Perseus Strategies, Robert F. Kennedy Human Rights, and Freedom House organizations, all of which represent her pro bono.

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It found Theary Seng’s detention arbitrary for several reasons, highlighting both the regime’s "political motivation" and that mass trials like Theary Seng’s "are incompatible with the interests of justice."

It noted that Theary Seng’s detention "is situated within a wider crackdown on freedom of expression," and that due process violations she faced were "designed to intimidate her into silence."

On June 5, while speaking to Cambodian garment factory workers, Hun Sen ruled out pardoning Theary Seng and publicly ordered his Justice Minister not to entertain any request for amnesty or sentence reduction for her.