Prime Minister John Key says his support for the Iraq war in 2003 was based on the information he and others had at the time.

Prime Minister John Key has stood by his 2003 support for the invasion of Iraq, after the release of a damning report into the bloody conflict.

A seven-year UK inquiry led by chairman Sir John Chilcot concluded the country's decision to join the US and go to war was based on flawed intelligence which over-hyped Iraqi dictator Saddam Hussein's supposed weapons of mass destruction.

As a first-term National MP in 2003, Key slammed the Prime Minister Helen Clark and her Labour-led government for failing to join the war, saying the country was "MIA" and had failed to back its traditional allies.

WPA Pool/Getty Images) Former UK prime minister Tony Blair has come under fire after the release of the Chilcot report.

"This country will pay for that - [MPs] need not worry about that," Key said at the time.

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Asked whether the Chilcot report showed he was on the wrong side of history, Key said he did not agree.

"I mean, hindsight is always a wonderful thing, and in hindsight, some of the information that was presented at the time was proven to be incorrect, but you don't know that - what you do know is is that all you can do is make the decisions based on the information you've got...

"At the particular time we made those comments, we were like the rest of the world, trusting of the information that Saddam Hussein had weapons of mass destruction and if that was the case, we believed that presented a very real threat to a great many people."

It was important to remember that Hussein was a "barbaric leader" who had killed "tens if not hundreds of thousands - maybe millions - of Iraqis", Key said.

'SADDAM WASN'T A GOOD GUY'

"He was a tyrant. In hindsight, obviously the information they had was wrong, but I don't think we should be recreating history that somehow Saddam Hussein was a good guy, because he wasn't."

Key said his government had an independent foreign policy, and did not make decisions based on any "special relationship" like that between the US and the UK at the time.

"We've sent trainers to Iraq because we believe that's the right thing to do, we've sent our SAS to Afghanistan because again, we believed that's the right thing to do, but we base it on the information we have at the time."

NZ First leader Winston Peters said the Chilcot report justified the decision not to go to war, and showed Key's "appalling" understanding of geopolitical events.

"The major lesson is not to lie to the public," Peters said.

Labour leader Andrew Little said the report's conclusions were predictable, and showed that Clark's judgement at the time was correct.

"I'm very proud to be the leader of the party that in New Zealand, while in government held off, didn't enter that conflict and stuck to its principles of internationalism, supporting the UN and saw no reason to get into that conflict."