Peter Mandelson has suggested that a wider international consensus should have been forged ahead of the Iraq war.

Speaking at a Progressive Governance conference in Hungary, the incoming EU trade commissioner also urged the next American president to rebuild ties with Europe.

Mandelson, a close ally of Tony Blair, said the extent of the current insurgency in Iraq could have been lessened if a second resolution authorising the war had been adopted.

Attempts at the United Nations security council in New York to achieve consensus on authorising the war broke down despite frantic last minute diplomacy by the British government.

But the former Cabinet minister said the current rebellion would have been a "lesser problem" if agreement had been reached at the UN.

"Who can doubt that the insurgency in Iraq would today be a lesser problem had a second resolution been agreed and the United Nations been in the driving seat from the start and throughout," he said.

"International legitimacy is what we urgently need to recover to secure progress in Iraq."

He also expressed caution about the use of the pre-emptive action in future.

Mandelson said the policy "is not one that can be applied scientifically, especially when intelligence on which we base judgments can neither be certain or precise".

But he added that western governments "cannot abandon all possibility of pre-emption".

And as European governments await the outcome of November's US presidential election, Mandelson had words of advice for the winner.

"A more internationalist United States and a more united and effective European Union... is the essential partnership that must be recreated by whomever goes into the White House next," he said.