Ken Livingstone, the former mayor of London, was accused of being "anti-American" in a leaked email from the US envoy to Britain.
The comment from the ambassador, Robert Tuttle, was included in a lengthy telegram sent to the US Transport Secretary, Mary Peters, briefing her on the British political scene ahead of her visit to London in December 2007.
It warned her of a dispute between the mayor and the ambassador over whether embassy staff should pay London's congestion charge. During the dispute, Mr Livingstone had described the ambassador as "a chiselling little crook".
Mr Tuttle claimed in his telegram, which was published yesterday on Wikileaks: "Ken Livingstone has focused his ire publicly against the US embassy and the ambassador personally. His position, however, should be seen in the wider context of his anti-American positions on many issues and his coziness to the likes of Hugo Chávez and Fidel Castro."
The ambassador also compared Gordon Brown, who had recently become the Prime Minister, with Tony Blair. He wrote: "Prime Minister Brown is much less outgoing than Blair and wishes to avoid being accused – as Blair was – of being President Bush's 'poodle', but he wants – and knows that Britain needs – a strong relationship with the US."
In 2007, Livingstone signed a deal with President Chávez under which London's buses and trams received cut-price fuel from Venezuela in return for advice on recycling and other issues.
His dispute with the US embassy hinged on whether the £8-a-day congestion charge was a tax.