The Tories have joined criticism of American policy in post-war Iraq and renewed their calls for a full-scale inquiry into the conduct of the conflict and its aftermath.
Shadow foreign secretary William Hague said attacks on US strategy from former British generals strengthened the case for such a probe.
But Downing Street insisted there had already been three "pretty exhaustive" inquiries into the war and consideration of lessons to be learned should wait until after British troops had withdrawn.
Mr Hague told Sky News Sunday with Adam Boulton: "We do think there have been many mistakes made. We would like to see a full-scale inquiry. I think some of the comments from one or two of the retired generals very much do strengthen the case for that and we want to see a full report when it gets back on Iraq,"
He said of post-war American policy: "I think many of the judgments they came to were wrong. They clearly underestimated the number of troops that would be needed for an effective occupation force. Very crucial mistakes have been made. Understanding those and making sure they are not repeated in the future is one of the reasons we have to have that inquiry."
Major General Tim Cross, the most senior UK officer involved in the post-war planning, said that Washington's policy had been "fatally flawed".
He also insisted he had raised serious concerns about the possibility of the country sliding into chaos with Donald Rumsfeld - but the then-US defence secretary "dismissed" the warnings.
Gen Cross's comments, in an interview with the Sunday Mirror, emerged after the former head of the Army, General Sir Mike Jackson, branded the American approach "intellectually bankrupt".
Sir Mike, who was in charge at the time of the 2003 invasion, also singled out Mr Rumsfeld for criticism, saying his claim that US forces "don't do nation-building" was "nonsensical".
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A Downing Street spokesman said there had already been three inquiries into the Iraq war which had been "pretty exhaustive". He said the Prime Minister had already acknowledged there were lessons to be learned, but that should wait until the military phase of the campaign was over.
