Barack Obama on Wednesday consolidated his lead with a thumping win in Mississippi but failed to attract white voters as the Democratic Presidential contest was hit by a fresh race row with a Hillary Clinton aide saying that the African American Senator had benefited from his colour.

Obama, 46, who is attempting to be the first black American to be elected to the Oval office, bagged at least 17 of the 33 delegates at stake while Clinton got 11.

People in Mississippi joined 'millions of Americans from every corner of the country who have chosen to turn the page on the failed politics of the past and embrace our movement for change', said Obama, who has 1,596 delegates, including separately chosen party officials known as 'superdelegates'.

It is the second straight defeat for Clinton, who scored stunning victories in Ohio and Texas last week to salvage a dying campaign. She now has 1,484 delegates.

However, neither of the two is expected to reach the score of 2,025 required to secure the Democratic nomination at the party's national convention this summer.

Exit polls showed that three-fourth of white voters supported Clinton, 60, while nine in 10 blacks voted for Obama in a racially polarised ballot.

Clinton supporter Geraldine Ferraro, meanwhile, set off another bitter verbal duel between the rival campaigns.

"If Obama was a white man, he would not be in this position," the Democratic nominee for vice president in 1984 told the Daily Breeze.

"And if he was a woman he would not be in this position. He happens to be very lucky to be who he is."

Obama called the remarks as 'patently absurd' but the campaign was baying for Ferraro's scalp pointing to the swift resignation of an Obama aide last week after her remark that Clinton was a 'monster'.

In a later interview, Ferraro defended her comments.

"Any time anybody does anything that in any way pulls this campaign down and says, let us address reality and the problems we are facing in this world, you are accused of being racist, so you have to shut up," she said.

But later she told Fox News she was not acting as a Clinton representative and that 'I am sorry that people thought it was racist.'

Clinton, however, distanced herself from the remarks.

"It is regrettable that any of our supporters on both sides ... say things that kind of veer off into the personal," she said.

In an e-mailed statement, campaign manager Maggie Williams echoed Clinton, who is bidding to be the first woman president of the United States.

Even before the counting began in Mississippi, the candidates were in Pennsylvania for the April 22 showdown where 158 delegates are at stake.

The nomination is, however, likely to rest in the hands of nearly 800 'superdelegates', who are now under enormous pressure from the two campaigns.