Prime Minister Hun Sen on Sunday confirmed the authenticity of a recorded telephone conversation with CNRP President Kem Sokha last year in which Mr. Sokha appears to distance himself from his partner at the time, former opposition leader Sam Rainsy.

“It was my real voice,” Mr. Hun Sen told government mouthpiece Fresh News on Sunday, apparently unperturbed by a raft of leaks that have left few ruling CPP and opposition leaders unscathed. “I wish to inform the public that his excellency Kem Sokha actually followed my advice.”

The 21-minute phone recording was posted on Saturday to the “Sei Ha” Facebook page that has hosted a number of leaks unflattering to the opposition. A spokesman for the opposition CNRP said he believed Mr. Hun Sen’s claim that the conversations were authentic, and said that the party was “not concerned” that apparent collaboration between Mr. Sokha and Mr. Hun Sen would damage the party’s credibility.

The conversation appeared to occur on the eve of the Pchum Ben festival in late September, when Mr. Hun Sen declared a “cease-fire” after months of attacking Mr. Sokha. The then-deputy president had been hiding in the CNRP’s Phnom Penh headquarters since May to avoid a court case the party criticized as being politically motivated, and was eventually granted a royal pardon supported by Mr. Hun Sen in December.

In the leaked conversation, Mr. Hun Sen lays out requests for Mr. Sokha to sideline Mr. Rainsy’s role as his counterpart and tone down opposition attacks against Mr. Hun Sen and his family—two outcomes that eventually came to pass.

“If you still want to be involved [with Mr. Rainsy], you will also be in danger,” Mr. Hun Sen warns. “Don’t forget that I am not afraid, even if the U.S. brings troops to Cambodia.”

Later in the conversation, Mr. Hun Sen advises Mr. Sokha to take over as president from Mr. Rainsy, referring to the former leader with the pejorative title of “ah.”

“I don’t want to destroy the CNRP—I want a partner in the CNRP, and I hope you will be able to work with me,” he said, with no response from Mr. Sokha.

Mr. Rainsy, who faces a slew of court cases of his own, resigned from the CNRP last month, after the CPP hastily pushed through an amendment to the Law on Political Parties barring convicts from leadership positions. His factional rival Mr. Sokha officially took over duties as CNRP president on Thursday, leading to a congratulatory letter from the prime minister.

At other points in the conversation, Mr. Hun Sen vows that Mr. Sokha won’t be arrested if he leaves the CNRP office to register to vote. Mr. Sokha registered on October 5 before promptly returning to the headquarters.

For his part, Mr. Sokha asks the prime minister to intervene in the court case against him, which centered on his failure to appear in court for questioning related to a sex scandal that itself was revealed through leaked audio.

Mr. Hun Sen says he can help only once Mr. Sokha’s verdict is finalized.

“Let’s find a time to meet at my house in order to organize a clear scenario,” Mr. Hun Sen said.

The prime minister also asks Mr. Sokha to post a message to Facebook before Pchum Ben making a public plea for civility in political discourse. He was incensed at ongoing rumors, which he claims were spread by Mr. Rainsy, that his eldest son Hun Manet was fathered by a Vietnamese communist official.

“I cannot accept it either,” Mr. Sokha said. “It should not be OK to say that.”

Mr. Sokha said that his daughter Kem Monovithya, the opposition party’s deputy head of public affairs, also discouraged the rumor.

Mr. Sokha went on to post a Facebook update on September 25 urging party members to “avoid using violent, rude or attacking words.” Ms. Monovithya slammed Mr. Rainsy in a series of tweets in October, telling reporters at the time that “the show must go on, it’s just not one about Peter Pan.”

CNRP spokesman Yim Sovann said on Sunday that the recordings were of no concern to the party.

“Everyone knows that there were negotiations and discussions between Kem Sokha and the prime minister, so this is not new,” he said. “The way that he handled that conversation…was very good.”

Mr. Rainsy said in an email on Sunday that the leaked conversation was an attempt to divide the opposition party.

“The other side cannot find any means to weaken the CNRP, they desperately resort to cheaper and cheaper tricks,” he said.

Political analyst Cham Bunthet, an adviser to the Grassroots Democracy Party, was less convinced, citing perennial distrust between grassroots factions aligned with Mr. Sokha and those with Mr. Rainsy, whose two parties combined in 2012 to form the CNRP.

“This is a big test for the new leadership,” he said on Sunday. “The marriage will be easily divorced if they do not manage this properly.”

(Additional reporting by Ben Paviour)

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