U.S. Attorney General John Ashcroft has joined the list of top U.S. administration members who are struggling to defend the war in Iraq amid mounting criticism that no weapons of mass destruction have ever been found.

On Monday, Ashcroft told reporters in Vienna that Saddam Hussein's past use of "evil chemistry" and the threat it posed justified the war. He said Hussein's weapons arsenal remained a menace and was sufficient cause to overthrow his regime.

"Weapons of mass destruction, including evil chemistry and evil biology, are all matters of great concern, not only to the United States, but also to the world community," he said.

U.S. Vice President Dick Cheney also defended the war Monday, saying Hussein harboured terrorists.

"Today the former dictator (of Iraq) sits in captivity; he can no longer harbour and support terrorists, and his long efforts to acquire weapons of mass destruction are at an end," Cheney told Italian political and business leaders in the Italian Senate.

British Foreign Secretary Jack Straw also insisted Britain's decision to join the war was justified, though he added it was disappointing that no banned weapons had ever been unearthed.

"I believe the decision we made on March 18 to take military action was justified then in terms of enforcing international law and is still more justified now," Straw told BBC Radio.

"A great deal more evidence will emerge."

White House press secretary Scott McClellan responded to reporters' questions on whether there are stilll banned weapons in Iraq by saying that inspectors need to continue searching.

"We believe it's important for the Iraq Survey Group to complete its work so we have as complete a picture as possible. ... It will help us learn the truth," he said.

On Friday, the chief U.S. weapons hunter in Iraq, David Kay, stepped down, saying he doubted Iraq possessed unconventional weapons.

"I don't think they exist," Kay told National Public Radio. "The fact that we found so far the weapons do not exist -- we've got to deal with that difference and understand why."

Kay says it appears Iraqi scientists presented Hussein with fanciful plans for weapons programs -- then used Hussein's money for other purposes. Kay says U.S. intelligence agencies didn't seem to realize this at the time and now owe U.S. President George Bush an explanation.

Critics including Democratic presidential candidates have jumped on Kay's comments and resignation, stepping up their charges against the Bush administration over the missing weapons.

"They ought to be held accountable for using the weapons of mass destruction argument," Democratic candidate John Kerry of Massachusetts said on Sunday on CBS' "Face the Nation" programme.

"Dick Cheney and others in the administration misled the American people with respect to the true status of the weapons of mass destruction in Iraq."

Cheney and U.S. Secretary of State Colin Powell recently held open the possibility that weapons would never be found.

Calling terrorism "the antithesis of freedom," Ashcroft said it remained a global menace and that "we see no nations as immune to the al Qaeda terrorist threat."

Middle East expert Robin Wright told Canada AM Monday that Kay's resignation is going to continue to cause trouble in Washington.

"There are likely to be a lot of questions as a result of David Kay's comments and his resignation -- calls for intelligence to be investigated. Because, after all, it was very solid U.S. intelligence data -- at least that's what the administration claimed, that led the United States to argue that Saddam Hussein had to be toppled."

She adds that the issue could mushroom for Bush as his party prepares for the November election.

"Domestically, the polls indicate he's not in trouble. Elsewhere in the world, the United States is dealing with deep skepticism about the president's claims.

"But both the weapons of mass destruction issue and the issue of creating a successful democracy in Iraq are likely to become a real focus once you get the candidates selected and the campaign launched after Labour Day. Both of these are likely to rise to the forefront of the campaign."