Jailed opposition leader Kem Sokha may not face trial until after the July elections, after a Phnom Penh Municipal Court decision on Monday to extend his pre-trial detention up to another six months.

Meng Sopheary, Sokha’s lawyer, confirmed that Investigating Judge Ky Rithy extended the former Cambodia National Rescue Party president’s detention, saying he needed more time to complete the investigation into Sokha’s alleged “treason” charges.

“The investigative judge decided to extend the detention for another six months,” Sopheary said. “The reason he gave was the investigation was not completed.”

She added that the defence continued unsuccessfully to seek his release on bail, citing Sokha’s health problems. In February, the defence team said Sokha had a pinched blood vessel and other ailments that needed treatment in Singapore.

“He [Sokha] was concerned that the symptoms would deteriorate if there is no proper treatment,” she said. “He also told us that he would not run away, even if someone told him to run away.”

Sokha was arrested in a midnight raid on September 3 and provisionally charged with “treason”. His party was summarily dissolved in November on similar grounds by the Supreme Court for allegedly plotting a purported “revolution”.

Over the course of his six months in prison, many opposition members have fled the country, with the vast majority of the CNRP’s elected positions being absorbed by the ruling party.

Officials have offered little evidence to substantiate the accusations beyond a years-old video of Sokha telling an audience of supporters in Australia that he received advice on his political career from the United States.

Monday’s hearing was conducted by Judge Rithy and Prosecutor Seang Sok at the remote Trapaing Phlong Prison in Tbong Khmum, where Sokha has been held since September, with the exception of a bail hearing last month in Phnom Penh, where his request for release was rejected.

Sopheary said Rithy attempted to question Sokha on the facts of the case being made against him, but that the opposition leader refused to answer them because he had already responded to such a line of interrogation. “The lawyers will file complaint to the Appeal Court against the decision to extend his detention,” she said.

The prospects of any pardon for Sokha and other targeted CNRP officials dimmed, with Hun Sen warning in a speech he would not extend another olive branch to the former opposition leader.

Political commentator Lao Mong Hay said there was little chance Hun Sen would release Sokha ahead of the elections because it would undo the premier’s campaign to subdue opposition supporters and get rid of the CNRP.

Additionally, the release of Sokha before July could become a rallying point for supporters, he said. “A trial before the election would further undermine the legitimacy of the election. A trial after the election would not affect its results,” he said.

Former CNRP lawmaker Mu Sochua said the continued detention of Sokha, given his health, was not a “risk that the authorities should take”, adding he should be let go with ample time to contest the July poll. “They cannot release him a day before the elections. They have to allow the CNRP to contest the elections and have time to prepare.”

Updated: 6:47am, Tuesday 6 March 2018