The former Fox News host claimed Mr Johnson wanted a $1m fee (around £793,000) to talk to him. However, Mr Johnson's team said he accepted this offer on the basis the money would go to Ukrainian charities.

Mr Johnson ultimately pulled out of the interview after the murder of Russian opposition leader Alexei Navalny, it is understood.

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Mr Carlson made the claim in an extended attack during an appearance on right-wing news channel Blaze TV.

The US presenter said he had been "annoyed" after Mr Johnson denounced him as a Kremlin stooge following his interview with Russian President Vladimir Putin.

He claimed he asked the former Tory MP for a talk and a member of Mr Johnson's team said "it's going to cost you one million dollars" and "then he will explain his position on Ukraine".

Mr Carlson denied supporting Mr Putin's regime, but added: "I'm not defending Putin, but Putin didn't ask for one million dollars... This whole thing is a freaking shakedown."

He said: "If you're making money, money off a war, you know, you can deal with God on that, because that's really immoral."

A spokesman for Mr Johnson said: "This account is untrue."

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The former prime minister's team said Mr Carlson, an influential voice in right-wing US media known for having launched scathing attacks against Ukrainian President Volodymyr Zelenskyy, had offered one million dollars for an interview on his channel.

Mr Johnson initially accepted, providing the money went solely to Ukrainian veteran charities, but decided not to go ahead with it after the death of Mr Navalny, which has been widely blamed on the Kremlin, they said.

It is the latest flare-up in a row between the pair after Mr Johnson used his Daily Mail column to brand Mr Carlson "a traitor to journalism" for his interview with the Russian president.

The 54-year-old was the first Western journalist to interview the authoritarian leader since Russia invaded Ukraine nearly two years ago.

Mr Johnson said the presenter had betrayed "viewers and listeners around the world" for not taking Mr Putin to task for "the torture, the rapes, the blowing up of kindergartens" in Ukraine.

The interview had seen the Moscow leader insist Mr Johnson helped scupper a deal aimed at ending the war - a claim that has been denied by the former MP and rubbished by senior Ukrainian figures.