Sorawong Thienthong, who also serves as Thailand's tourism minister, said in a Facebook post that the prime minister would not quit, despite growing calls for her resignation after her apparent mishandling of a border dispute with neighbouring Cambodia.

"The prime minister has clearly confirmed to us that she will continue to perform her duty to resolve various crises that the country is facing to the best of her ability," he said.

"The government confirms that it will continue to work, not resign, and not dissolve parliament."

Paetongtarn, daughter of divisive tycoon and former premier Thaksin Shinawatra, is facing domestic anger over the leak of a phone call between her and Cambodia's influential former leader Hun Sen, in which she appeared to kowtow before the veteran politician and denigrated a senior Thai military commander.

The Bhumjaithai Party, which was the second-biggest partner in Thailand's ruling coalition, withdrew from the alliance late on Wednesday, citing the leak earlier that day.

Another coalition member, the United Thai Nation party, looked set to demand Paetongtarn's resignation in return for backing the Pheu Thai-led ruling coalition and securing its narrow parliamentary majority.

Paetongtarn has apologised for the call with Hun Sen, but not commented on the crisis so far.

Activists have also scheduled a protest in Bangkok starting on June 28 to ask for Paetongtarn's resignation, among them groups with a history of influential rallies against Shinawatra administrations.