Top Barack Obama aide quits after calling Hillary Clinton a 'monster'

Harvard professor Samantha Power resigned following an interview in which she said Mrs Clinton would stop at nothing to beat Obama in the race for the Democratic presidential nomination.

"She is a monster, too - that is off the record - she is stooping to anything," said Miss Power, who is a Pulitzer Prizewinning journalist for her reporting from Bosnia.

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"You just look at her and think: 'Ergh'. But if you are poor and she is telling you some story about how Obama is going to take your job away, maybe it will be more effective.

"The amount of deceit she has put forward is really unattractive."

The attack by 37-year-old Miss Power is a major embarrassment for Obama who has insisted his campaign will be above personal attacks.

He bitterly complained about negative tactics after he lost primaries in Texas and Ohio this week in a setback to his hopes of contesting the November election with Republican candidate John McCain.

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The Irish-born professor, who likes to tell the tale of how she played basketball with George Clooney, was a key member of Obama's foreign policy team and one of his closest aides.

Her basketball playing friends call her the Tower of Power.

If Obama makes it to the White House, Miss Power - who was cited by Men's Vogue as one of the most beautiful women in the world - was expected to take a crucial role in redefining the Anglo-American relationship.

Miss Power had tried to withdraw the comments she made to The Scotsman newspaper - but she had agreed in advance that her interview would be conducted on the record.

After she quit, she said she "deeply regretted" the remarks, adding: "These comments do not reflect my feelings about Senator Clinton, whose leadership and public service I have long admired.

"I should not have made these comments. It is wrong for anyone to pursue this campaign in such negative and personal terms. I apologise to Senator Clinton and to Senator Obama, who has made very clear that these kinds of expressions should have no place in American politics."

The uproar overshadowed the news that Obama raised more than £27million in funds in February, the biggest amount ever collected in a presidential campaign.