US senators have again delayed a vote on President George Bush's nomination of John Bolton as ambassador to the UN, to examine new allegations against him.
Bolton denies being a serial abuser of underlings
The vote by the Senate Foreign Relations committee is now due to take place in May to allow fresh hearings.
The decision came after Republican Senator George Voinovich indicated he would side with the Democrats who oppose Mr Bolton's nomination.
He has been accused of being a poor manager and influencing intelligence.
"I think we all ought to get more information on this man," Mr Voinovich said on Tuesday.
"I've heard enough today that I don't feel comfortable about voting for Mr Bolton," he added.
Republicans had been ready to push the controversial nomination through the committee on a party-line vote.
The vote had been previously postponed to allow Democrats to call more witnesses.
Yale Law School graduate
As assistant secretary of state under George Bush senior, helped organise anti-Saddam alliance
Made under-secretary of state for arms control and international security in May 2001
In July 2003, condemned North Korean leader Kim Jong-il for living like royalty while people lived in "hellish nightmare"
The Democrats say Mr Bolton - who is currently the top US diplomat for arms controls and a well-known critic of the UN - has abused junior members of staff and tried to force intelligence analysts to shape their reports to reflect his views.
The Washington Post newspaper said Mr Bolton had withheld sensitive information about Iran from both his former boss and the current Secretary of State, Condoleezza Rice.
But the Republican chairman of the committee had backed Mr Bolton in a public statement.
Senator Richard Lugar said the concerns about him did not "warrant our rejection of the president's selection".
Republicans hold 10 seats on the Senate panel to the Democrats' eight, and while two Republican senators have expressed some doubts about the nominee, neither has said he will vote against Mr Bolton.
If he is approved by the committee, the nomination goes to the full Senate, which has a Republican majority.
Secretary of State Rice has praised Mr Bolton.
She said Mr Bolton - a vocal critic of the UN - would be a strong proponent for change at the organisation.
When asked by correspondents whether accusations that he was a serial abuser stood up, she said: "It's certainly not the John Bolton that I know or that a lot of other people know."
Mr Bolton has denied trying to have people who disagreed with him sacked.