Thailand's Foreign Ministry summoned the Cambodian ambassador on Thursday to deliver a protest letter, following a leaked phone call between Prime Minister Paetongtarn Shinawatra and Cambodia's Senate President Hun Sen discussing border issues.

At a news conference on Thursday, Thailand's Foreign Minister Maris Sangiampongsa said the public disclosure of the private conversation "undermined the trust and respect between the two leaders and countries".

Earlier, Foreign Ministry spokesman Nikorndej Balankura said the leaking of the conversation, without consent from the prime minister, amounted to a disrespectful act toward Thailand.

The recording captured Paetongtarn referring to a Thai military commander, who oversees a disputed border area on the Thai side, as her opponent, a remark that sparked fierce criticism on social media. Both Thailand and Cambodia have been trying to ease tensions and border disputes recently.

Paetongtarn apologized for the leak on Thursday, explaining that the informal call was made from her personal phone and her government stands ready to support the country's military in all ways.

On Wednesday, Hun Sen explained on social media that, as is customary, in order to avoid any misunderstanding or misrepresentation in official matters, it was necessary to record the conversation for the sake of transparency, including for internal purposes.

Only about nine minutes of the call have been posted publicly, he said, while the conversation was shared with about 80 individuals to avoid any misunderstanding or misrepresentation in official matters, Cambodia's state AKP news agency reported.

Thailand's conservative Bhumjaithai Party, the second-biggest partner in the ruling coalition, pulled out on Wednesday, saying Paetongtarn's conduct in the leaked call had wounded the country and the army's dignity.

It said its executive board unanimously agreed to exit the government. All of the party's ministers have tendered their resignations to the prime minister, effective from Thursday.

Two other coalition parties, the United Thai Nation and the Democrat Party, have scheduled meetings to discuss the situation later on Thursday. Losing either would put Paetongtarn's government, formed in August, in danger of an abrupt collapse.

Border tensions between Thailand and Cambodia have mounted recently after soldiers of both countries briefly exchanged gunfire in a disputed border area, resulting in the death of a Cambodian soldier. They have yet to reach agreements on four remaining unsettled sections of their border.

Xinhua and agencies contributed to this story.

yangwanli@chinadaily.com.cn