Irish-born aide to US Democratic presidential candidate Barack Obama, Samantha Power, stepped down from the campaign today amid uproar over a comment she made to a British newspaper referring to Democratic rival Hillary Clinton as a "monster."
"She made the decision to resign and we accepted it," said Robert Gibbs, Mr Obama's communications director.
Ms Power had been an aide to Mr Obama in his Senate office before signing on to advise his presidential campaign on foreign policy issues 14 months ago.
The comment threatened to become a huge embarrassment for Mr Obama, who has criticized what he calls negative campaign tactics by Ms Clinton and has based his presidential bid in part on a theme of rising above political bickering.
Mr Obama, an Illinois senator, and Ms Clinton, a New York senator, are locked in a drawn-out battle for the Democratic nomination for the November presidential election.
The furor erupted over Ms Power's comments to British newspaper The Scotsmanthat were published today. The newspaper made clear that Power had said that she did not want the comment attributed to her.
"She is a monster, too - that is off the record - she is stooping to anything," Ms Power said of Ms Clinton.
"We f***** up in Ohio," she said. "In Ohio, they are obsessed and Hillary is going to town on it, because she knows Ohio's the only place they can win."
Ms Clinton defeated Mr Obama in nominating contests in the large states of Ohio and Texas on Tuesday to keep her campaign alive after a string of losses to Obama.
Before the news that she was quitting, Ms Power issued an apology, and Mr Obama condemned the comment through his campaign.
"These comments do not reflect my feelings about Senator Clinton, whose leadership and public service I have long admired," Ms Power said.
"I should not have made these comments and I deeply regret them. It is wrong for anyone to pursue this campaign in such negative and personal terms.
I apologize to Senator Clinton and to Senator Obama, who has made very clear that these kinds of expressions should have no place in American politics."
Ms Power is the founding executive director of the Harvard University Carr Center for Human Rights policy.
Mr Obama campaign spokesman Bill Burton said "Senator Obama decries such characterizations which have no place in this campaign."