Cambodia's influential ex-premier Hun Sen on Friday accused Thailand's prime minister of insulting the Thai king, as tensions between the neighbouring countries intensified.

He said Prime Minister Paetongtarn Shinawatra's comments about her military commander – who she labelled an "opponent" – in a leaked phone call with the veteran leader over a border dispute were "an insult to the king".

In a livestream on his official Facebook page, Hun Sen said: "An insult to a regional commander is an insult to the Thai king because it is only the king who issued a royal decree to appoint him."

The daughter of controversial ex-premier Thaksin Shinawatra – who goes on trial for lese-majeste next week – faces being sacked as prime minister as the phone call scandal has triggered calls for her to step down and her government to teeter.

Hun Sen – father of Cambodia's prime minister Hun Manet and former close ally to Thaksin – last week posted the full 17-minute recording of the private conversation on his official Facebook page.

"I just let Thailand know how the prime minister committed a dirty act to their nation," he said on Friday.

In the recording posted online, the two leaders discussed restrictions imposed on border crossings after a military clash last month killed a Cambodian soldier.

Thailand has strict lese majeste laws, which bans criticism of King Maha Vajiralongkorn and his close family and carries sentences of up to 15 years in jail per offence. (AFP)