Blair's strong support for the U.S.-led invasion was the most controversial and possibly the most unpopular of his 10 years in power.
"I am truly sorry about the dangers that they (British forces) face today in Iraq and Afghanistan," Blair said.
"I know some may think that they face these dangers in vain; I don't and I never will. I believe they are fighting for the security of this country and the wider world against people who would destroy our way of life.
"Whatever view people take of my decisions, I think there is only way view to take of them: they are the bravest and the best."