Nigel Farage has branded a controversial poster urging black and ethnic minorities to vote as a "disgusting" example of "sectarian politics".
The poster, released by Operation Black Vote, features "an elderly Asian British woman being berated by an aggressive thug".
The campaign says it is meant to show everyone has the same voting power.
The UKIP leader accused Operation Black Vote, who he said he had previously supported, of "trying to divide society".
He said: "I want to engage people in all communities to get involved in our democracy but I'm afraid this poster is a really big mistake."
The ad was designed by Saatchi and Saatchi.
Magnus Djaba, chief executive of Saatchi and Saatchi London, said: "This is a message about democracy, not a message about race. Whichever community you're from, it hits home."
Operation Black Vote said there are about four million Black and Minority Ethnic voters and a further 400,000 citizens of Commonwealth countries entitled to take part in the referendum - but about 30% are not registered to vote.