Tony Blair is being urged to make a statement to the House of Commons to answer claims that the Government exaggerated the threat posed by Iraq's "weapons of destruction."
Iain Duncan Smith says the allegations risk undermining the credibility of Britain's intelligence services.
The call comes as Downing Street attempts to quell the growing political storm by indicating that a parliamentary committee is already looking at the issue.
In a letter to Mr Blair, the Tory leader said: "Serious allegations are now being made, allowing others to cast doubt on statements made by you and your ministers following upon it.
"My concern is that this will have a detrimental affect on the ability of the Government and the Armed Forces to complete their task in Iraq, unless things are cleared up quickly."
Mr Blair has already rejected claims that the Government "sexed-up" intelligence on Saddam Hussein's weapons, a stance he is expected to underline when questioned by MPs in the Commons on Wednesday.
But Mr Duncan Smith said the gravity of the issue required "urgent and detailed answers."
Downing Street said the Parliamentary Intelligence and Security Committee already had the issue "in hand."
But Labour MPs voiced concern that the committee, which reports to the Prime Minister and not Parliament, would not provide full independent scrutiny of the facts.