History will judge whether the government was right to go to war with Iraq, Jack Straw has told Labour MPs.
Mr Straw said he believed the war was entirely justified
But the foreign secretary insisted he thought the decision was "entirely justified" because it was taken to topple a "brutal dictator".
That contrasts with Tony Blair insisting last year that his government had no policy of "regime change".
He said war was necessary to neutralise the "serious" threat from Saddam Hussein's weapons of mass destruction.
On Sunday the prime minister conceded for the first time that he was no longer sure whether any weapons of mass destruction would be found in Iraq.
But in an address to the Parliamentary Labour Party foreign affairs committee, held behind closed doors, Mr Straw steered clear of predicting whether the Iraq Survey Group would find evidence of such weapons.
He said: "For 12 years, Iraq refused to comply with mandatory demands from the United Nations to answer the many questions none of us could afford to let go unanswered.
"The issue was quite simply too important for us to walk away from.
"The decision to go to war to overthrow a brutal dictator, who continued to threaten his own people and his neighbours, was entirely justified.
"As the people of Iraq take control of their own affairs and experience the freedom and prosperity denied to them for so long, I am very content for history to be our judge."
Mr Straw said he welcomed progress towards decommissioning weapons programmes in Libya and Iraq and he urged other countries developing nuclear, biological or chemical weapons to think again.
That was taken to be a message directed at North Korea.
Libya's leader Colonel Muammar Gaddafi's decision to announce that his country was giving up its weapons of mass destruction programmes was of "profound importance", said Mr Straw.
And Iran had shown a "new willingness to engage with the international community on the nuclear issue".
"Military action must always be the option of last resort. And, in recent
months, we have seen that the vital issue of WMD can be dealt with by diplomatic
means - but only where a partner exists with whom we can negotiate," said Mr
Meanwhile the BBC has been told that the US government "twisted, distorted, simplified" intelligence about weapons of mass destruction in a way that led Americans to "seriously misunderstand what the threat was.
Greg Thielmann, director of the Strategic Proliferation and Military Affairs Office at the US State Department until his retirement last year, said President George W Bush's administration had "seriously misled" US citizens over the weapons threat.
Mr Theilmann said he was disappointed that Mr Blair had not confronted the US over its use of intelligence material.
His comments followed those from former US treasury secretary Paul O'Neill who claimed that Mr Bush had planned the invasion of Iraq from the moment he came to power.