Jailed former opposition leader Kem Sokha has lost his final bid for bail as he awaits trial on a charge of “treason” – an allegation widely believed to be politically motivated.

The Supreme Court today ruled his detention was justified and upheld a decision of the lower court, but did not provide clear reasoning for its decision.

Sokha, former president of the now-dissolved Cambodia National Rescue Party, was arrested at midnight on September 3 and has spent the past six months detained in a remote prison in Tbong Khmum province, near the Vietnam border.

His party was forcibly dissolved by the Supreme Court in November, just months before this year’s national election, with 118 of the party’s members banned from undertaking political activities for the next five years.

Seven of Sokha’s eight lawyers made lengthy verbal appeals to the Supreme Court judges this morning. One, Chan Cheng, referred to Sokha’s ongoing health issues, including diabetes, high blood pressure and a shoulder injury.

“I am very worried about his health. If he dies in the prison…then it will go down in history as the first death of a political prisoner in jail since 1979,” Cheng said.

He added that denying bail – a decision which would look like “collusion” with the authorities – could have dire results. “My client would die…[and] the courts are responsible,” he said.

But the judges were not swayed, with Supreme Court Judge Kim Sathavy saying “the health treatment must be based on the available resource in the country”. “If the detainees want to have the health services, there must be permission from the prosecutor,” she added.

This week Sokha’s pre-trial detention was extended for a further six months, meaning he is not likely to be tried until after July’s national poll.

Sokha’s arrest stemmed from the circulation from an edited video of a speech he gave in Australia in 2013, in which he talked about the role of democratic grassroots movements in overthrowing regimes at the ballot box and the political advice he received from the United States.

Last month Sokha was brought to Phnom Penh for his unsuccessful Appeal Court hearing, but Supreme Court Prosecutor Ouk Kimseth yesterday said Sokha would not be brought for Friday’s verdict. “The Supreme Court only decides on the legalities of the case, so the presence of the accused is not important,” he said.

Sokha’s failed bid for release comes during a visit from United Nations Special Rapporteur Rhona Smith, who on Wednesday was denied a request to visit Kem Sokha in his Tbong Khmum prison cell. Smith said she was “disappointed” by that decision and reminded Cambodian authorities “should not deny me access to any detainees”.

The ASEAN Parliamentarians for Human Rights renewed their call for Sokha’s release last week.

“These trumped-up charges should never have been brought in the first place. They should be immediately dropped and Kem Sokha unconditionally freed,” the group's chairman, Charles Santiago, said last week.

The government has countered that Sokha's arrest was a matter of “life or death” for the country.