US President George W Bush is facing fresh charges that he exaggerated the threat of Iraq's alleged weapons of mass destruction to win support for the war.
There is no conclusive evidence of weapons of mass destruction
In a strong attack on Mr Bush's administration, Democratic Senator John Kerry accused the president of misleading everyone.
Mr Kerry, a leading contender to contest the 2004 presidential election for the Democrats, promised that Congress would get to the bottom of the matter.
Committees in both houses of the US Congress are continuing private inquiries into the issue, but on the ground in Iraq no stocks of weapons of mass destruction (WMD) have so far been found.
The Bush administration built its case for war around its contention that Iraq had WMD, and has recently faced increasing political and public questioning of its motives.
"He misled every one of us," Senator John Kerry said, claiming this was one reason he was running for the presidency.
"I will not let him off the hook throughout this campaign with respect to America's credibility and credibility to me because if he lied he lied to me personally," Mr Kerry said, speaking in new Hampshire.
The Vietnam veteran is one of nine Democratic presidential hopefuls
However a senior Pentagon official, Douglas Feith, stressed that the weapons would be found.
The current lack of substantial evidence of a weapons programme did not mean that the war was wrong, Mr Feith told the BBC.
"It's clear to us that we're going to learn what is happening in the country, in particular what's the situation regarding the weapons of mass destruction, we think, mainly from individuals who are knowledgeable, rather than from any kind of attempt to spot-check the country through inspections.
In another development, US Defence Secretary, Donald Rumsfeld, suggested Washington is willing to consider making deals with captured senior members of Saddam Hussein's administration, to help the hunt for weapons of mass destruction.
His comments came after British MPs suggested such a deal could be arranged in return for help in finding former the former Iraqi president, his sons, and weapons of mass destruction.
Earlier, the capture was announced of Abid Hamid Mahmud al-Tikriti - Saddam Hussein's presidential secretary and one of his closest confidantes - the most senior figure to be detained to date.
President Bush has, meanwhile, defended UK Prime Minister Tony Blair who is facing what correspondents say is his biggest challenge in his six years in power over accusations that he embellished intelligence reports to support his case for war.
This nation acted to a threat from the dictator of Iraq. Now there are some who would like to rewrite history; revisionist historians is what I like to call them
"[Tony Blair] operated on very sound intelligence, and those accusations are simply not true, Mr Bush said.
He said those who accuse Mr Blair of exaggerating the threat from Iraq before the war were wrong.
The BBC's Justin Webb in Washington says Mr Bush seems to be frustrated, even annoyed by the British debate on weapons of mass destruction and perhaps concerned that a similar row could engulf him as well.