Melody Townsel, a Texas public relations executive, could cause President George Bush the first defeat of his second term. Her evidence about the behaviour of John Bolton, one of Mr Bush's favourites, looks increasingly likely to scupper his appointment as US ambassador to the UN.

Melody Townsel, a Texas public relations executive, could cause President George Bush the first defeat of his second term. Her evidence about the behaviour of John Bolton, one of Mr Bush's favourites, looks increasingly likely to scupper his appointment as US ambassador to the UN.

Republicans on the Senate Foreign Relations Committee, already uneasy about reports of the nominee's persistent bullying and short temper, delayed a confirmation vote after Ms Townsel told them Mr Bolton screamed and shouted at her in a Moscow hotel more than a decade ago. She now believes he is unfit to represent the US.

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Ms Townsel, who runs her own agency in Dallas, told The Independent on Sunday that Mr Bolton had banged on her hotel room door and ranted at her over a two-week period in 1994. He also made disparaging remarks about her weight, accused her of theft and even questioned her sexuality.

"I was alone in the hotel room. It was easy for him to drop by and bang on the door, trying to pressure me until I broke," she said. "Several times a day he would pound on the door and shout 'This is not going to go away. I don't know what you're doing.' "

The alleged harassment occurred when Ms Townsel was working as a contractor for the US Agency for International Development (USAid) on an advertising campaign supporting privatisation in Kyrgyzstan. Mr Bolton, currently the Bush administration's senior official on arms proliferation, was then a lawyer in private practice. She said she had written a letter to USAid complaining about a lack of funding from the main contractor, a company called International Business and Technical Consulting which Mr Bolton was representing, and claims he was sent to force her to retract her complaint.

"There are a number of points I would make about this," she added. "His temper was just one of them. I believe he was pursuing his client's interests, but a number of the things he said could have been career-shattering."

The allegations of Ms Townsel, a self-described liberal, add to a growing picture of Mr Bolton as an aggressive and often domineering figure, ready and willing to bully staff under him. Carl Ford, a former State Department intelligence analyst, previously told the Senate committee that he considered Mr Bolton a "serial bully" after witnessing his behaviour towards another analyst who refused to alter his assessment of Cuba's weapons ambitions. It was also revealed last week that the former secretary of state, Colin Powell, has privately expressed his concern about Mr Bolton's temperament.

Ms Townsel's comments, which she initially revealed in a letter to the Senate Foreign Relations Committee, had the effect last week of postponing the confirmation process for several weeks. Senator George Voinovich, a Republican from Ohio, told the committee he was concerned that Mr Bolton's behaviour did not meet the standards required.

The White House has said it stands behind Mr Bolton and expects to see him confirmed. "John's distinguished career and service to our nation demonstrates that he is the right man at the right time," Mr Bush said. But the dilemma for the administration now is whether to cut its losses - a reflection of the growing perception that he does not have the temperament for such a senior diplomatic role - or dig its heels in.

But Ms Townsel may not be finished yet. She says she is preparing an affidavit that will detail all of Mr Bolton's behaviour, both in Moscow and after she returned to Kyrgyzstan, and will send it to the committee, which is now due to vote on 12 May.