Jailed former opposition leader Kem Sokha was questioned by a judge in prison yesterday, according to his lawyers, who classified the questioning as “aggressive” and “inappropriate”.

Kem Sokha was arrested in early September and later charged with “treason” based on a 2013 video in which he talks about receiving assistance from the United States in political planning. Following this, his Cambodia National Rescue Party – the only viable competitor to the long-ruling Cambodian People’s Party – was dissolved by the Supreme Court last month over government accusations that it was fomenting a foreign-backed “colour revolution”, and more than 100 senior CNRP officials were banned from politics for five years.

Ky Rithy, Phnom Penh Municipal Court investigating judge, interrogated Sokha for the second time at Trapeang Plong Prison, near the Vietnamese border in Tbong Khmum province.

Lawyer Pheng Heng said the judge asked inappropriate questions about the politician’s family’s private life.

“There was a question asking when his daughter started being involved with a foreigner. And when will she get married? It is their privacy and it is not appropriate … It should not be asked in this case,” he said.

The anonymous Facebook account “Kon Khmer” in August began circulating unsubstantiated conspiracy theories – many of them republished by government mouthpiece Fresh News – featuring photos of the family with foreigners. It also accused Sokha’s daughters, Kem Monovithya and Kem Samathida, of colluding with US spies.

The post said that Monovithya was dating US Embassy official Sam Downing, whom it claimed was a CIA agent, and that Samathida had a “close relationship” with alleged “spy” Geoffrey Cain. Cain, who is actually a successful American freelance journalist, again categorically denied allegations yesterday.

“I’m not a spy. That is a fabricated allegation to build fake evidence against the opposition party,” he said. The allegations against him were among the purported evidence cited in the Supreme Court’s CNRP dissolution hearing.

The investigating judge’s line of questioning, Cain said, “shows the court is desperate to get Kem Sokha convicted”.

Monovithya agreed yesterday. “It is harassment,” she said.

Lawyer Heng also accused the judge of only asking questions designed to incriminate, instead of also considering possible exculpatory evidence, as is the norm in civil law systems.

Heng added that Sokha continued to reject all allegations.

Judge Rithy could not be reached yesterday, but Justice Ministry spokesperson Chhin Malin said the judge’s questioning was part of a strategy. “All the questions are according to scientific and physchological technique,” he said.

Another lawyer for Sokha, Chan Chen, said the judge would return to conclude his questioning on Thursday or Friday next week.