Tony Blair does not regret the Iraq war despite the "nightmare" it unleashed, but feels "desperately sorry" for those who died, the former British prime minister said in memoir.
"A Journey", Blair's account of his decade in Downing Street from 1997 to 2007, also includes an unprecedented attack on his "strange" successor Gordon Brown, whose premiership he branded a disaster.
It details the personal toll the job took on him, including his use of whisky, gin and wine as a "prop", the "animal" feelings he had for his wife, and his relationship with the royal family after princess Diana died.
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But it is Blair's decision to take Britain into the US-led invasion of Iraq that lies at the heart of the 718-page book.
He suggested he had wept over the soldiers and civilians killed in the thrust to overthrow Saddam Hussein, writing: "Tears, though there have been many, do not encompass it.
"I feel desperately sorry for them, sorry for the lives cut short... to be indifferent to that would be inhuman, emotionally warped."
But he reiterated that he "can't regret the decision to go to war," adding: "All I know is that I did what I thought was right."
He also acknowledged that the turmoil that followed the March 2003 invasion was far worse than anticipated.
"The aftermath was more bloody, more awful, more terrifying than anyone could have imagined," he said. "I can say that never did I guess the nightmare that unfolded."
In a BBC interview to publicise the book, Blair said the international community should now be prepared to consider taking military action against Iran if it develops a nuclear weapon.
"I am saying that I think it is wholly unacceptable for Iran to have a nuclear weapons capability and I think we have got to be prepared to confront them, if necessary militarily," he said.
Blair also gave candid insights on the "huge strain" life in Downing Street put on him, his lawyer wife Cherie and their four children, the youngest of whom was born while he was in office.
He used alcohol as a "prop" to relax and was "at the outer limit" of the regular intake limit advised by doctors.
"Stiff whisky or G & T (gin and tonic) before dinner, couple of glasses of wine or even half a bottle with it," Blair wrote. "So not excessively excessive. I had a limit. But I was aware it had become a prop."
He also wrote in intimate detail about one night with Cherie when he was preparing to try for his party's leadership.
"On that night of 12 May 1994, I needed that love Cherie gave me, selfishly" he wrote.
"I devoured it to give me strength, I was an animal following my instinct, knowing I would need every ounce of emotional power and resilience to cope with what lay ahead."
The memoirs also feature revelations about high-profile figures, with Blair admitting he was a "sucker" for princess Diana but that Queen Elizabeth II had treated him with "hauteur" in the days after Diana's death in 1997.
He told of "trying" visits to Balmoral, the royal family's Scottish retreat, when the queen had donned rubber gloves to do the washing up after the royals' traditional barbecue for staff and guests.
Elsewhere, Blair made public as never before the private tensions which simmered between him and the "maddening" but "brilliant" Gordon Brown, his long-serving finance minister and successor as premier.
He described Brown -- who was ousted in May elections -- as a "strange guy" with "zero" emotional intelligence, and had thought his premiership would be "terminal" for the longest-running Labour government in British history.
"It is easy to say now, in the light of his tenure as prime minister, that I should have stopped it; at the time that would have been well nigh impossible," Blair wrote.
Blair, who reportedly received a 4.6 million pound (5.6 million euro, 7.2 million dollar) advance for the book, will donate all proceeds to the Royal British Legion, a charity helping war veterans.
His memoirs are being published in English worldwide this week and translation rights have been sold to 17 territories.
Within hours of its release, online seller Amazon said "A Journey" was ranked first on its British bestseller list, and by Wednesday night bookseller Waterstone's said it had become their fastest selling autobiography.
Blair himself was in the United States, having been invited to a White House dinner by US President Barack Obama in his role as Middle East peace envoy.
