Prime Minister Gordon Brown admitted Monday it had been a "mistake" to fail to prepare adequately for rebuilding Iraq following the 2003 removal of Saddam Hussein.
But speaking days before his predecessor Tony Blair testifies to Britain's Iraq war inquiry, Brown -- who will face the probe himself within weeks -- insisted that the war was justified by a previous UN resolution.
"I think the mistake in the war was not to do the reconstruction and plan it in the way that was necessary so that Iraq could recover quickly after Saddam Hussein fell," Brown said at his monthly press conference.
Challenged about the legality of the 2003 US-led invasion, Brown said he would address such issues when he appears before the public inquiry into the war.
But he added: "As far as the war is concerned, I have always said that the UN resolution that said to Saddam Hussein for over 10 years that he had to take action to deal with the threat he was posing to other countries was a very decisive part of the reasons why we had to take the actions we did."
He is due to give evidence over the next few weeks, after Blair, who was prime minister at the time of the conflict, gives his eagerly awaited version of events on Friday.
Brown added: "I stand by all the actions I have taken and I welcome the chance to explain not only the circumstances in which our government made the decisions it did, but also the circumstances in which we brought our troops home from Iraq."
He had initially been expected to give evidence after the general election, which is expected to take place by June, but his offer to appear earlier was accepted.