The adverts also ridicule Mr Kerry's wife, Teresa Heinz Kerry, for boasting of her African roots. She was born and raised in Mozambique under colonial Portuguese rule.

In another, Mr Kerry is criticised for not voting on a bill to extend unemployment benefits, because he was campaigning.

"It lost by one vote," the advert says. "Maybe Kerry thought the more of us who are unemployed and hurting, the more likely we would vote Democrat."

The ads, which have infuriated the Kerry camp, are run by a Washington-based organisation called People of Colour United, backed by J Patrick Rooney, a white American who owns a medical insurance firm.

The company stands to profit from the prescription drug law passed last year by President George Bush.

Mr Rooney told the Washington Post: "I support [the] group because the genuine word from the black community should be heard, not white folks saying it for them."

African-American support is crucial to the Democratic party, which won more than 80% of the black vote in 2000.

Mr Kerry's deputy campaign manager, Bill Lynch, said: "It's disgusting that the president's political allies are now using race as a political weapon."

But Republicans and critics in the black community claim the Democrats have been taking the black vote for granted.

Virginia Walden-Ford, who runs People of Colour United, said she was perturbed by African-Americans who say that they will vote Democrat "because we are Democrats".

"That is a bad way to vote. I want people to be informed," she said.