South Korean President Yoon Suk Yeol has accused the country’s media of damaging its alliance with the United States after a TV broadcaster released a video suggesting that he insulted US congress members following a meeting with Joe Biden in New York last week.

MBC caught Mr Yoon on tape talking to his aides and top diplomats following a brief chat with his US counterpart Mr Biden on the margins of the UN General Assembly meetings.

While the audio was unclear, Mr Yoon could be heard using what seemed to be indecent language during comments the broadcaster captioned as: “Wouldn’t it be too darn embarrassing for Biden if those idiots at legislature don’t approve?”

Mr Yoon’s meeting with Mr Biden came after they both delivered speeches in support of the Global Fund, an international campaign to fight Aids, tuberculosis and malaria.

The Biden administration has pledged six billion dollars (£5.53 billion) in US contributions to the initiative through until 2025, but this is pending congressional approval. Mr Yoon’s government has promised 100 million dollars (£92 million).

After the MBC video roused the internet and triggered criticism from rival politicians decrying a “diplomatic disaster”, Mr Yoon’s office denied the report hours later on Thursday, insisting that he was not talking about the US congress or Mr Biden.

Kim Eun-hye, Mr Yoon’s spokesperson, said the president was expressing concern that South Korea’s opposition-controlled National Assembly could reject his plans for the 100 million dollar contribution.

She said that the word MBC heard as “Biden” was actually “nal-li-myeon”, an expression that can be used to describe something being thrown away. She did not specifically address Mr Yoon’s apparent use of a word that could be translated as “idiots”.

Talking to reporters in Seoul on Monday after wrapping up his trip in Canada, Mr Yoon stuck with his office’s version of the story. He said that the media could put South Korea’s security in danger by “damaging the alliance with reports that differ from facts”.

Mr Yoon called for a need to find the “truth” behind the reports that described him as insulting American legislators, while leaders of his conservative People Power Party threatened to take action against MBC.

“MBC’s actions have become difficult to just stand back and watch,” said Joo Ho-young, the party’s floor leader. “If (Yoon) used a word about the United States as described in the initial MBC report, that would have required thorough fact checking considering the consequences to South Korea-US relations.

“But MBC skipped this verification process and aired the report with arbitrary and very provocative captions.”

Mr Joo said the party would take “various measures” against MBC, including protest visits and demanding the broadcaster disclose the circumstances surrounding its report.

MBC is one of the country’s largest terrestrial channels. While the company operates on advertising revenue, its largest shareholder is a public organisation whose chairperson is appointed by the government.

Lee Jong-bae, one of the People Power Party’s members in the Seoul Metropolitan Council, filed a complaint against MBC to Seoul police, accusing the broadcaster of defamation and disrupting presidential duties.

The party spokesperson, Park Jung-ha, questioned whether MBC was aligned with members of the liberal opposition Democratic Party, which holds majority in South Korea’s parliament, in a supposed attempt to rattle Mr Yoon’s government.

Yoon and his party’s harsh response to the MBC report comes as he faces criticism that he returned with underwhelming results from his foreign trip, which included the funeral of the Queen, the UN meetings and a visit to Canada for a summit with Prime Minister Justin Trudeau.

Much of the attention before the trip was about whether Yoon would meet Biden to discuss contentious bilateral issues, including South Korean frustrations over the recently passed US Inflation Reduction Act that excludes South Korean electric vehicles and other models assembled outside of North America from consumer tax credits.

The liberal opposition labelled Mr Yoon’s diplomacy as a failure after his chat with Mr Biden following their Global Fund speeches lasted less than a minute. Seoul’s foreign ministry said Mr Yoon still “sufficiently conveyed” South Korean concerns over the new law to Mr Biden.

MBC did not immediate respond to calls for comment. Mr Yoon has not specifically addressed whether he was insulting South Korean legislators following his meeting with Mr Biden.