PHNOM PENH (Reuters) - A Cambodian court convened on Wednesday to begin the trial of opposition party leader Kem Sokha on charges of treason in a case that has drawn condemnation from rights groups as a move by longtime leader Hun Sen to crush political rivals.

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Diplomats packed the Phnom Penh Municipal Court amid tightened security, and reporters were not allowed to view the proceedings after the morning court session.

“Between 1993 until now, Kem Sokha planned and implemented a secret plan in collusion with foreigners to overthrow the royal government,” Cambodian Judge Koy Sao said as he read the charges to Sokha.

The judge said Sokha had conspired with American and Canadian advisers on regime change, like that of Yugoslavia and Serbia, before playing a video clip from 2013 in which Sokha suggested he had received political advice from unspecified Americans.

Sokha rejected the video clip as evidence, saying that his version of the video had him saying he wouldn’t stage a revolution.

“This video isn’t complete, the content is out of context, it has been edited ... I have my own video, will the court play it? Has the court verified this video?” Sokha said.

Several countries and institutions were named in the case, including the European Union (EU), USAID, the United States and Canada, as were individuals like President Donald Trump and Senator Ted Cruz.

It could take up to three months to deliver a verdict, defense lawyers said on Tuesday, meaning the case could still be in progress by the time the EU makes a decision next month on whether to cut Cambodia’s preferential trade status over its human rights record.

Kem Sokha was arrested in 2017 and his opposition Cambodia National Rescue Party was banned ahead of a 2018 election, in which the party of Hun Sen won all the parliamentary seats.

He was freed from house arrest in November but a ban on his engaging in political activity was kept in place.

Kem Sokha’s daughter Monovithya Kem called the trial against her father a “farce”, and rights groups urged the case to be dismissed.

“Kem Sokha will be the victim of a staged trial on completely bogus treason charges,” said Phil Robertson, deputy Asia director of New York-based Human Rights Watch.

Many other opposition figures have fled into exile and have accused Hun Sen, who has ruled Cambodia for 35 years, of establishing a one-party state.

The EU, which accounts for nearly half of Cambodia’s exports, will decide in February whether to remove Cambodia from its Everything But Arms trade scheme over the crackdown on political expression.