Race became a focus of the Democratic presidential campaign on Sunday after Hillary Clinton accused Barack Obama of distorting remarks she made last week about the 1960s US civil rights movement.
In an NBC television interview, Ms Clinton was asked about remarks to Fox News last Monday, which some had interpreted as giving former president Lyndon Johnson more credit than black leader Martin Luther King for advancing the landmark 1964 Civil Rights Act.
Hillary Clinton
Mr Obama said Mrs Clinton had offended some Americans who felt her comments last Monday had marginalised the role of Mr King in advancing civil rights.
"The Obama campaign is deliberately distorting this," said the New York senator (60) and former first lady yesterday.
"Dr King didn't just give speeches. He marched. He organised. He protested," Ms Clinton said.
"And he campaigned for political leaders including Lyndon Johnson because he wanted someone in the White House who would act on what he had devoted his life to achieving.
Mr Obama said he had never commented on her previous statement but said it had "offended some folks who felt that somehow diminished Mr King's role in bringing about the Civil Rights Act.
"She is free to explain that, but the notion that somehow this is our doing is ludicrous," he said.
Mr Obama (46) has garnered support among blacks, who make up about 13 per cent of the population, but the Clintons have long had strong support from the black community.
Democrats are preparing for contests in Nevada next Saturday and South Carolina on January 26th, while Republicans are focused on Michigan on Tuesday and South Carolina.