President Bush was dealt a blow by senators from his own party last night when they asked for a delay to the ratification vote on John Bolton, the Republican nominee for UN ambassador, because of new abuse allegations.

The Senate Foreign Relations Committee, which has a Republican majority, had been expected to approve Mr Bolton's nomination.

But it decided to delay the vote until next month after Senator George Voinovich of Ohio stunned fellow Republicans on the committee. "I’ve heard enough today that I don’t feel comfortable about voting for Mr Bolton today," he told them.

Democrats on the committee have been waging a battle against Mr Bolton, the State Department’s arms control chief, arguing that his alleged bullying of subordinates makes him unsuitable for the sensitive UN role.

Much of Mr Bolton’s two-day confirmation hearing last week focused on claims that he targeted lower-level State Department employees who disagreed with his views.

Some accusers have approached the committee independently. Melody Townsel, a Dallas businesswoman, claimed that an angry Mr Bolton chased her through a Russian hotel and threw objects at her during a conference a decade ago.

In a letter, she said he was "genuinely behaving like a madman. I eventually retreated to my hotel room and stayed there. Mr Bolton then routinely visited me to pound on the door and shout threats."

After the meeting, Senator Voinovich said he had changed his mind after an impassioned critique from Senator Christopher Dodd, a Connecticut Democrat.

"The passion on the other side on this, I don’t think, is political," he said. "I think they raised some legitimate issues. I think we ought to find out what they are, I think we ought to get the information, get a chance to have (the allegations) rebutted," he said.

Two other Republicans also opposed voting yesterday: Senator Lincoln Chafee of Rhode Island, who had previously expressed doubts and Chuck Hagel of Nebraska, who gave warning that he may not support Mr Bolton’s nomination if it did move to the full Senate.

"The dynamic has changed. A lot of reservations surfaced today. It’s a new day," Senator Chafee said.

Democrats have uncovered other allegations about Mr Bolton's personal dealings and Senator Joseph Biden of Delaware said they have found instances where Mr Bolton’s Senate testimony did not seem to agree with the facts.

Last week, Senator Biden said that appointing Mr Bolton as UN ambassador would be like "sending a bull into a china shop".

Despite the new allegations, the Bush Administration is standing by Mr Bolton. There was no indication that he might withdraw his name, but it was clear his nomination was in trouble.

Scott McClellan, White House press secretary, said some Democrats were continuing to raise unfounded allegations. "We believe John Bolton has addressed all these issues. He’s testified for more than eight hours," he said.

"He’s responded to many questions in writing as well, and we look forward to addressing any questions the committee members continue to have."

Senator Barbara Boxer of California hoped Mr Bush would nominate someone else for the job. "Surely there must be many other men and women who could fulfil this post with honour."

No new date for a vote has been set by the Senate committee, but it is not likely for at least two weeks. Democrats plan to use the delay to investigate the new allegations.

Mr Bolton may be asked to return to give further testimony and the committee may also now call additional witnesses, Democrat senators said.

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