One of Rupert Murdoch's leading pundits on the Fox News television channel, Bill O'Reilly, has become embroiled in the latest public row over the depiction of black people in the mainstream media.

O'Reilly, who describes himself as a populist and traditionalist, has been accused of "velvet racism" for comments on his radio show about the famous Harlem restaurant Sylvia's. The remarks referred to a dinner the commentator had enjoyed there with the Rev Al Sharpton, the black preacher and political leader.

The dinner itself passed off uneventfully, by all accounts. But when O'Reilly reminisced about the evening he portrayed it in a way that set alarm bells ringing across the blogosphere.

He started out by praising the staff and largely black clientele of the restaurant for being "very, very nice" and "tremendously respectful". Warming to his theme, he said: "I couldn't get over the fact that there was no difference between Sylvia's restaurant and any other restaurant in New York City. I mean, it was exactly the same, even though it's run by blacks."

To compound matters, in a separate radio broadcast he referred to the dinner again. "There wasn't one person in Sylvia's who was screaming, 'M-Fer, I want more iced tea.' You know, it was like going into an Italian restaurant in an all-white suburb. People were sitting there, and they were ordering and having fun. And there wasn't any kind of craziness at all."

O'Reilly insists he was making positive points about the American melting pot - a common theme of his radio and television shows in which he frequently lambasts "race-based" activists such as Mr Sharpton. But the tone of surprise in his voice, and the implication that he had previously assumed black restaurants to be less civilised than their white counterparts, has caused outrage. As a black law professor, Anita Allen of Pennsylvania University, put it to ABC News: "He doesn't realise dinner can be a civilised affair and we do use table napkins."

The furore is the latest evidence that previously untouchable rightwing talkshow hosts are now vulnerable to scrutiny as a result of blogs. The pundit's comments were publicised by the liberal monitoring website Media Matters, which pointed to previous O'Reilly remarks including a 2005 broadcast in which he said many poor residents of New Orleans failed to evacuate the hurricane-stricken city because "they were drug-addicted".

O'Reilly will be aware of the fate of his fellow rightwing controversialist Don Imus, who was sacked by CBS five months ago when he referred to a black women's basketball team as "nappy-headed hos". Imus, who was also exposed by new media activists, has yet to be taken back on air.

The issue of how black people are represented by the media, as well as by themselves in terms of racial slurs by black rappers and comedians, reached Capitol Hill this week when a congressional committee opened a hearing entitled From Imus to Industry: the business of stereotypes and degrading images.

A senior Fox executive said the latest row was "nothing more than leftwing outlets stirring up false racism accusations for ratings". O'Reilly himself sought to dampen the row by claiming his words were taken out of context.

Paul Waldman of Media Matters fired back: "If Bill O'Reilly got caught robbing a bank he would say he was taken out of context."