Cabinet minister Peter Hain has described the US government as the "most right-wing" in living memory.
Peter Hain has previously criticised the Bush administration
In an interview with the New Statesman magazine, Mr Hain, a deputy leadership contender, said President George Bush's foreign policy has "failed".
He also said that Labour's foreign policy "achievements" had been "forgotten" because of the Iraq war.
Mr Hain, Northern Ireland Secretary, has previously been critical of Mr Bush, but these comments go further.
Mr Hain, who is also Welsh secretary, said: "The neo-con mission has failed.
"It's not only failed to provide a coherent international policy, it's failed wherever it's been tried, and it's failed with the American electorate, who kicked it into touch last November."
He went on to say that: "The problem for us as a government ... was actually to maintain a working relationship with what was the most right-wing American administration - if not ever, then in living memory".
Mr Hain also told the New Statesman that all of Labour's foreign policy "achievements" had been forgotten because of the war in Iraq.
"All that we've achieved on the international agenda, whether it's trebling aid to Africa, or leading the fight for trade justice, or lifting billions in debt off the poorest countries, or whether it's a new arms export policy which imposes tough controls - all of Robin Cook's policy agenda, including the focus on human rights that he brought in - all of these things people have forgotten about because of the Iraq conflict."
Mr Hain was a Foreign Office Minister under Robin Cook.