An official US report saying Iraq had no weapons of mass destruction when US-led forces invaded has intensified the debate about justification for the war.
Duelfer confirmed there were no WMD stockpiles in Iraq
Democrat Senator Jay Rockefeller said thousands had died and yet Iraq had never posed a grave or growing danger.
However, the report by the Iraq Survey Group said there was evidence that Saddam Hussein intended to resume a weapons programme.
The White House said this showed the former Iraqi leader posed a threat.
UK Prime Minister Tony Blair said that while he now accepted that Iraq held no stockpiles of WMD ready to be deployed at the time of the invasion, the report showed that UN sanctions had not been working.
Australian Prime Minister John Howard, another leading member of the coalition, said the report had changed nothing and he was "not in any way apologetic" for being involved in the war.
The coalition used allegations of Iraqi WMDs as a key reason for going to war.
Chief US weapons inspector Charles Duelfer, who heads the ISG, said in the report that Iraq had no stockpiles of biological, chemical or nuclear weapons before last year's US-led invasion.
Iraq's nuclear capability had decayed not grown since the 1991 war, he added.
President Bush himself again defended last year's invasion, though he made no reference to the report.
On the election campaign trail on Wednesday, Mr Bush said that the world was better off without Saddam Hussein, and the risk of him passing weapons of mass destruction (WMD) to terror groups was "a risk we could not afford to take".
But Senator Rockefeller, who attended a closed-door briefing by Mr Duelfer before the publication of the report, completely disagreed.
"We invaded a country, thousands of people have died and Iraq never posed a grave or growing danger," he said.
World opinion also remains divided over the report.
Iraq's Deputy Prime Minister, Barhem Saleh, said anyone who doubted that Saddam Hussein had WMDs only needed to visit Halabja - where the former Iraq dictator had gassed thousands of Kurds.
IRAQ SURVEY GROUP
Set up in May 2003
First leader, David Kay, quit in Jan 2004 stating WMD would not be found in Iraq
New head, Charles Duelfer appointed by CIA
1,200 experts from the US, Britain and Australia
HQ in Washington, offices in Baghdad and Qatar
But former chief UN weapons inspector Hans Blix said he hoped Mr Blair and Mr Bush would now admit that the invasion of Iraq was a mistake.
Key findings in the report:
- "The ISG has not found evidence that Saddam possessed WMD stocks in 2003, but [there is] the possibility that some weapons existed in Iraq, although not of a militarily significant capability."
- "There is an extensive, yet fragmentary and circumstantial body of evidence suggesting that Saddam pursued a strategy to maintain a capability to return to WMD after sanctions were lifted... "
- "The problem of discerning WMD in Iraq is highlighted by the pre-war misapprehensions of weapons which were not there. Distant technical analysts mistakenly identified evidence and drew incorrect conclusions."
The ISG also published a list of people and groups to whom Saddam Hussein allegedly offered cheap oil in return for their support in trying to get UN sanctions lifted.
Many on the list - drawn from official Iraqi documents - are from Russia, France and China - countries which opposed the war in Iraq.