Tony Blair has faced fresh challenges over his justification for the war in Iraq.

The US official in charge of Iraq contradicted the prime minister over the existence of Saddam Hussein's deadly arsenal of weapons.

Paul Bremer rejected Blair's claim that the Iraq Survey Group had found "massive evidence" of a weapons programme as a "red herring".

"That is not what David Kay [head of the Iraq Survey Group] has said," Bremer told ITV.

"It sounds like a bit of a red herring to me. It sounds like someone who doesn't agree with the policy sets up a red herring then knocks it down."

And former foreign secretary Robin Cook also tackled the prime minister's comments.

"It is undignified for the prime minister, and worrying for his nation, to go on believing in a threat which everyone else can see was a fantasy," he wrote in the Independent.

"Nor will Tony Blair ever recover his credibility until he stops insisting he is right when the public can see he was wrong."

He was joined by Dr David Hope, the Archbishop of York, who warned the prime minister would have to answer in the end to God.

"Undoubtedly a very wicked leader has been removed but there are wicked leaders in other parts of the world," he said.

And Dr Tom Wright, the Bishop of Durham, described Blair as a "vigilante".

"For Bush and Blair to go into Iraq together was like a bunch of white vigilantes going into Brixton to stop drug dealing," he said."This is not to deny that there's a problem to be sorted, just that they are not credible people to do it."

Blair was also criticised by a senior diplomat in London for breaking a promise to speed up the extradition of terrorist suspects.