Thousands of protesters have gathered in the Thai capital Bangkok, calling for the resignation of Prime Minister Paetongtarn Shinawatra after a phone call she had with the former Cambodian leader Hun Sen was leaked.

In the call, which was about a recent incident on their border, she addressed Hun Sen as “uncle” and said a Thai military commander handling the dispute “just wanted to look cool and said things that are not useful”.

The call has sparked public anger. Paetongtarn apologised, but defended the call as a “negotiation technique”.

Before leaving to visit flood-hit northern Thailand, Paetongtarn told reporters it is the people’s “right to protest, as long as it’s peaceful”.

Saturday’s rally was the largest of its kind since the ruling Pheu Thai party came to power in 2023.

Thousands braved the monsoon rain and blocked the roads at the Victory Monument war memorial in Bangkok, waving Thai flags and holding placards with slogans such as “PM is enemy of state”.

Protest leader Parnthep Pourpongpan said the prime minister “should step aside because she is the problem”.

Seri Sawangmue, 70, travelled overnight by bus from the country’s north to join the protest.

He told AFP news agency that he was there “to protect Thailand’s sovereignty and to say the PM is unfit”.

“I’ve lived through many political crises and I know where this is going,” he added.

Paetongtarn has said she will no longer hold future calls with the former Cambodian leader, but Parnthep told Reuters that many Thai people felt she and her influential father were being manipulated by Hun Sen.

Paetongtarn, 38, is the daughter of Thaksin Shinawatra, the deposed former prime minister who returned to Thailand last August after 15 years in exile. She has only been in office for 10 months and is the country’s second female prime minister, with the first being her aunt Yingluck Shinawatra.

Protesters are calling for the end of Shinawatra leadership.

The rally was organised by a coalition that has protested against Shinawatra-led governments for more than two decades.

The group said in a statement read to crowds that the executive branch and parliament were not working “in the interest of democracy and constitutional monarchy”, Reuters reported.

As well as the flags and placards, people carried umbrellas to protect themselves from the rain. When it stopped, a rainbow formed over Victory Monument.

On Tuesday the Constitutional Court will decide whether to take up a petition by senators seeking Paetongtarn’s removal for alleged unprofessionalism over the Hun Sen call.

Hun Sen said he had shared the audio clip with 80 politicians and one of them leaked it. He later shared the entire 17-minute recording on his Facebook page.

The call was about a recent dispute between Cambodia and Thailand, which saw tensions increase in late May after a Cambodian soldier was killed in a border clash, plunging ties to their lowest in more than a decade.

But the tension between the two nations dates back more than a century, when the borders were drawn after the French occupation of Cambodia.

Both have imposed border restrictions on each other, while Cambodia has banned Thai imports from food to electricity, as well as Thai television and cinema dramas.

Despite the tensions between their countries, the Shinawatras’ friendship with the Hun family goes back decades, and Hun Sen and Paetongtarn’s father consider each other “godbrothers”.