Prime Minister Hun Sen on Wednesday slammed opposition figure Sam Rainsy’s claim that the former president of his court-dissolved Cambodia National Rescue Party (CNRP) will be “released” next month. He said such a development would happen when “the horse grows horns”.

Kem Sokha, the former CNRP leader, was arrested in September last year on charges of “conspiring with a foreign power” to allegedly overthrow the Hun Sen government.

He spent a year in pre-trial detention before his release on bail to his home in Phnom Penh. Observers have said his bail restrictions are so strict they amount to “house arrest”, while the government has hailed the court’s decision as a “humanitarian” act due to his poor health.

Charged under Article 443 of the Criminal Code, Sokha, 65, is facing 15-30 years behind bars.

Former CNRP leader Rainsy, who is now president of the Cambodia National Rescue Movement, made the contentious posting on his Facebook page on Tuesday evening.

Citing a ruling Cambodian People’s Party (CPP) “internal source”, he said Sokha would be “released” on December 29 – the day the ruling party marks the 20th anniversary of Hun Sen’s “Win-Win” policy – after being found guilty in a “bogus trial” and given a royal pardon.

The “Win-Win” policy of 1998 is credited with helping bring the remnants of the Khmer Rouge to engage with the government and so finally end 20 years of civil war.

Speaking to more than 23,000 garment workers in Takeo province’s Bati district on Wednesday, the prime minister hit out at Rainsy, calling him a “liar” and a “cheat”.

He said as Sokha’s treason case had not resulted in a conviction, no pardon could be granted.

Hun Sen said: “Sam Rainsy posted on Facebook, saying that on December 29 Hun Sen will release Kem Sokha . . . the same day we celebrate the 20th anniversary of the ‘Win-Win’ policy, because of international pressure.

“[Opposition] supporters, please wait and see . . . your boss [Rainsy] is cheating you because [Sokha] has not been convicted yet – there is no sentence to pardon [him from].

“[Rainsy] doesn’t understand the law . . . Hun Sen does not have the right to sign documents requesting the King for [Sokha’s] pardon when he is under [legal] prosecution and the verdict has not been handed down. Now, I have a short message: ‘wait until the horse grows horns.’”

Rainsy, who lives in France to escape convictions seen by some as politically motivated, wrote on his official Facebook page late on Tuesday, citing a CPP “internal source”, that Sokha would be freed due to “international pressure”.

Rainsy claimed: “Kem Sokha to be released by the end of this year. The release …will take place on December 29, which will mark the 20th anniversary of Hun Sen’s ‘Win-Win’ policy in his dealings with the Khmer Rouge.

“But in order to ‘save face’ and prevent the reinstatement of the CNRP, Hun Sen wants to quickly organise a bogus trial.

“Faced with international pressure, the Cambodian government will shortly release Kem Sokha, leader of the opposition Cambodia National Rescue Party (CNRP), which was dissolved by Prime Minister Hun Sen in November 2017.

“But to prevent the reinstatement of the CNRP, dissolved under the accusation of ‘treason’ made against Kem Sokha, Hun Sen must get his ludicrous claims of ‘treason’ validated by a compliant court.

“After the organisation of a bogus ‘trial’, the inevitable guilty verdict will be immediately followed by a royal pardon.”

Hun Sen countered by accusing Rainsy, who regularly posts on social media, of attacking the government to purely attract Facebook “likes”, and claimed international pressure would not make him change his position.

“He posts only to attract ‘likes’. But his posts only make [things worse] for him. He posts lies,” Hun Sen said. “[He] says Hun Sen receives international pressure, then would release [Sokha].

“I say [to] this [that] Cambodia is an independent state.”

Analyst Hang Vitou said on Wednesday that attempts by Rainsy to “antagonise” Hun Sen are counterproductive.

“It’s like pouring oil on fire because the CPP has both [political] and financial power which they do not want to surrender. So using mockery or pressuring them will not be productive,” he said.

However, Vitou added that the government hitting out at criticism will not make Cambodians unite, but rather further “split” society.

“Only using [cool-headed] strategies will bring rewards,” he said.