A billboard, erected in Mason City, Iowa and funded by the North Iowa Tea Party, which depicts Barack Obama between Hitler and Lenin, has "crossed the line", according to other Tea Party activists in the state.

The billboard shows Hitler with the slogan "National Socialism" and Lenin with the legend "Marxist Socialism", and Obama in between the two under the phrase "Democratic Socialism". Each photograph carries the word "Change".

John White, co-ordinator of the Iowa Tea Party movement, said that his organisation had previously asked members to stop using similar posters.

"At our last rally we saw some people with these kinds of signs and asked people to put them down," he said, going on to call the erection of the billboard "a borderline hate crime".

So far, the North Iowa Tea Party has declined to comment on the erection of the billboard or its contents.