The first of 1,400 military experts have arrived in Iraq to begin a new search for evidence of weapons of mass destruction.
Blair says the charges are totally untrue
They arrived in Baghdad as a row continued to rage in the UK over whether the prime minister over-stated the threat posed by Iraq, to strengthen the case for war.
Tony Blair said he was confident the team, from the US, UK and Australia, would find signs of the nuclear, chemical or biological weapons.
"I have absolutely no doubt at all that they will find the clearest possible evidence of Iraq's weapons of mass destruction," he said.
The most senior American military official in Iraq, Lieutenant General David McKiernan, said while it may take some time to discover the weapons, the team would stay in Iraq for "as long as it takes".
No independent inquiry
Former Labour chancellor Lord Healey argued that Mr Blair should resign if he is wrong about weapons of mass destruction (WMD).
"If he is found out to have been wrong about those weapons - or worse, that he knowingly made false statements - I believe he should be replaced as leader," he said, writing in The Independent.
The Liberal Democrats are continuing to call for a full independent inquiry into whether intelligence documents on Iraq's weapons were changed on the orders of Downing Street to strengthen the case for military action.
The Tories kept up the pressure by tabling their own motion -
calling for a judicial investigation under the Tribunals of Inquiry
(Evidence) Act 1921 - which is expected to be debated next week.
On Wednesday the Lib Dems, backed by the Tories, were defeated in a motion calling for a judicial inquiry into the matter, by 301 votes to 203.
Mr Blair again insisted it was "completely and totally untrue" that a dossier had been "sexed up".
But he said he would allow the all-party intelligence and security committee (ISC) to conduct an inquiry into the row.
Conservative leader Iain Duncan Smith said the credibility of the government was now at stake.
BBC political editor Andrew Marr said Mr Blair seemed to have ridden the storm inside Westminster - but "outside, many people are still wondering whether this country went to war honestly".
The row began when an intelligence source told the BBC a claim made in a government dossier that Iraq could use weapons of mass destruction within 45 minutes had been given undue prominence by Downing Street.
In the Commons, Mr Blair backed a claim by cabinet minister John Reid that "rogue elements" in the intelligence services were briefing against the government.
But he said he was convinced that nobody from the Joint Intelligence Committee (JIC) - which briefs ministers on security matters - was involved.
Mr Blair said the disputed claim was entirely the work of the JIC.
On BBC2's Newsnight programme, another military source said to be "intimately involved" in the compilation of the dossier said he had been "uneasy" with the 45-minute claim.
The source, who the programme said could not be described as a "rogue
element", believed the emphasis placed on the claim had turned a possible capability into an imminent threat.
But he did not dispute the assertion that the intelligence services had put the claim into the dossier.
MPs on the influential foreign affairs select committee have already said they are to investigate the way the government presented intelligence information over Iraq's weapons.
Former foreign secretary Robin Cook said while he gave "two cheers" to the two investigations, he would have preferred "a more open and transparent inquiry", conducted by somebody from outside politics.
He said the probes should look at why the government got the assessments about the risks of Saddam's alleged WMD "so wrong".
Shadow Commons leader Eric Forth questioned the value of the ISC's inquiry, which will take place behind closed doors and over which the prime minister has editorial control.
But Mr Blair said its report would be published and his spokesman indicated that the prime minister himself could give evidence to the inquiry.