David Miliband has insisted British leaders did not indulge in "vainglorious boasting" after the 2003 invasion of Iraq.
Appearing before Sir John Chilcot's panel in central London, the foreign secretary said that complacent back-slapping was "shattered pretty quickly" as problems with post-war planning emerged.
Seven years after a US-led coalition ousted Saddam Hussein from Baghdad the country remains unstable, with yesterday's parliamentary elections marred by the deaths of 38 people in terrorist attacks.
Mr Miliband claimed that Britain's standing in the Arab world had been strengthened, rather than undermined, by its role in the Iraq invasion and its aftermath.
"I don't believe that the Iraq decisions have undermined our relationships or our ability to business. Some of our ambassadors say we are in stronger position," he suggested.
"The view of us is that we are seen to have played a part in freeing the country from a tyranny that is bitterly remembered."
Mr Miliband's comments on Iran strayed from the hardline warning made by former prime minister Tony Blair.
"I do not call Iran a rogue state but it is a state which continues to defy the international system," he said in today's session.
In an interview with the Telegraph newspaper published today, he said he had not lost any sleep over the Iraq war.
"I don't do sleepless nights, but you don't need the legal query you raise to know there are hard questions to be asked of anyone who supported the war," he admitted.
"It would be stupid to pretend the balance is all on one side of the ledger. We haven't lost the peace, but a lot of people have lost their lives... It was much easier to win the war than the peace."