In a speech on Friday, Blair insisted he was right to take the nation to war in Iraq.
"It remains my fervent view that the nature of the global threat we face in Britain and around the world is real," Blair said in his constituency of Sedgefield, northeast England.
"This is the task of leadership to expose it and fight it, whatever the political cost," Blair said.
"No decision I have ever made in politics has been as divisive as the decision to go to war in Iraq," Blair said. "It remains deeply divisive today," he added.
Blair said the September 11 attacks had come as a "revelation" to him and persuaded him of the need to act against rogue states.
"No decision I have ever made in politics has been as divisive as the decision to go to war in Iraq"
prime minister, UK
He played down a row over the confidential advice that his government was given shortly before the 20 March invasion that led to Saddam Hussein's downfall.
Clare Short, who quit as Blair's international development secretary last May in protest over the war, has alleged that Attorney General Lord Goldsmith was "leant on" to justify Britain joining the war in the absence of a final explicit UN Security Council resolution.
But Blair said this latest Iraq controversy was no more than an "elaborate smokescreen" which would soon be replaced by another row "then another and then another".
"The real point is that those who disagree with the war, disagree fundamentally with the judgment that led to war," Blair said.