Tony Blair has rejected as "completely absurd" suggestions that a dossier compiled by the government on Iraq's weapons of mass destruction was rewritten to make it "sexier".
Mr Blair met his Polish counterpart in Warsaw
The claims - made to the BBC on Thursday by a senior British intelligence official - emerged as the UK prime minister became the first Western leader to visit post-conflict Iraq.
Speaking in Poland where he was giving a speech on the EU, Mr Blair said Saddam Hussein's chemical, biological and nuclear weapons programmes were well documented by the United Nations and "not some invention of the British security services".
He said he had "absolutely no doubt" about the truth of the evidence about Iraqi weapons of mass destruction.
"What's more, the idea that we authorised or made our intelligence agencies
invent some piece of evidence is completely absurd."
Flanked by his Polish counterpart, Leszek Miller, the UK prime minister added he still believed the weapons would be found, but at the moment it was "not the most urgent priority" in post-war Iraq.
"Our priority having got rid of Saddam is to rebuild the country so the focus at the moment is on the humanitarian and the political reconstruction of the country," said Mr Blair.
"The threat from weapons of mass destruction with Saddam Hussein out is obviously not immediate anymore."
Mr Blair then turned on critics of US-led military action in Iraq.
He said: "People who have opposed this action throughout are now trying to find a fresh reason for saying why it wasn't the right thing to do.
"And I tell you that when you go to Iraq and you speak to the people there and you see the freedom they have and you see the liberty they have, you realise it was emphatically the right thing to do."
The dossier in question was published last September, and warned that Saddam Hussein had the capacity to activate his biological and chemical weapons in just 45 minutes.
Earlier this week US defence secretary, Donald Rumsfeld, suggested that the weapons might have been destroyed before the fighting began although he has since added that he personally believed they would be found.
The intelligence official told the BBC the dossier had been "transformed" a week before it was published on the orders of Downing Street.
He said: "The classic example was the statement that weapons of mass
destruction were ready for use within 45 minutes.
"That information was not in the original draft. It was included in the
dossier against our wishes because it wasn't reliable.
"Most things in the dossier were double source but that was single source and
we believe that the source was wrong."
But the official said he was convinced that Iraq had a programme to produce weapons of mass destruction, and felt it was 30% likely there was a biological weapons programme.
He said some evidence had been "downplayed" by chief UN weapons inspector Hans Blix.
But Iraqi scientists captured during the war had not provided much information as yet, he added.
Senior sources inside the British intelligence community told the BBC on Thursday night that the heads of every agency that contributed to the dossier were satisfied with its contents.
They were nervous, however, that this was the first time secret material had been used in this way to support the government's case so publicly, the sources added.
Downing Street said: "Not one word of the dossier was not
entirely the work of the intelligence agencies."
The BBC report said the Parliamentary Intelligence and Security Committee is to conduct an inquiry into the UK Government's claims about Saddam Hussein's regime.
Liberal Democrat foreign affairs spokesman Menzies Campbell said the report added weight to rumours that the intelligence services were unhappy about the way their evidence was being used.
Labour MP Tam Dalyell, who opposed the war with Iraq, called for a Commons statement on the claims.