Former British prime minister Tony Blair has said that he could not have imagined what he called the 'nightmare' that unfolded in Iraq.
However, he still did not regret joining the US-led invasion.
In his political memoir, Tony Blair echoed previous statements that the 2003 invasion was justified because Saddam Hussein posed a threat and could have developed weapons of mass destruction.
The 57-year-old said he felt 'desperately sorry' for the lives cut short, but said the mistaken belief that Saddam Hussein was hiding weapons of mass destruction was an 'understandable error'.
Controversial decision
'I can't regret the decision to go to war ... I can say that never did I guess the nightmare that unfolded,' said Mr Blair, referring to the years of political and sectarian bloodshed in Iraq that followed the invasion.
'I have often reflected as to whether I was wrong. I ask you to reflect as to whether I may have been right.'
Tony Blair was the closest ally of former US President George W Bush over the decision to invade Iraq.
The decision was the most controversial of Tony Blair's ten-year premiership.
It provoked huge protests, divisions within his Labour Party and accusations he deceived the British people over his reasons for war when weapons of mass destruction were not found.
'I feel words of condolence and sympathy to be entirely inadequate,' Tony Blair wrote of the war's casualties.
'They have died and I, the decision-maker in the circumstances that led to their deaths, still live.'
Pressure of office
Elsewhere in the book's 715 pages Mr Blair revealed a previously unknown reliance on alcohol to cope with the pressure of office.
He felt he was using drink as a 'prop', having a whiskey before dinner followed by a half a bottle of wine.
Tony Blair was damning about former finance minister Gordon Brown who succeeded him as prime minister in 2007.
He described his political rival as brilliant but lacking human instinct.
'Political calculation, yes. Political feelings, no. Analytical intelligence, absolutely. Emotional intelligence, zero.'
He blamed Gordon Brown for the Labour government's defeat in the May election after 13 years in power, saying it was a fatal mistake to move away from Mr Blair's centrist 'New Labour' policies.
Tony Blair, now an envoy for the Quartet of Middle East peacemakers - the US, Russia, the EU and the UN - was Labour's longest-serving prime minister, winning three consecutive elections before stepping down in 2007.
The self-penned volume, 'A Journey', was published on the day the US formally ended combat operations in Iraq after a conflict that claimed more than 100,000 deaths, most of them civilians.
He says he is donating the reported £4.6m (€5.5m) advance he received for his memoirs as well as proceeds from sales to a charity supporting serving and former members of the military.
Extracts from 'A Journey'
On the 2003 invasion of Iraq
'I can't regret the decision to go to war. Never did I guess the nightmare that unfolded, and that too is part of the responsibility.'
'Tears, though there have been many, do not encompass it. I feel desperately sorry for them, sorry for the lives cut short, sorry for the families whose bereavement is made worse by the controversy over why their loved ones died, sorry for the utterly unfair selection that the loss should be theirs.'
'I have often reflected as to whether I was wrong. I ask you to reflect as to whether I may have been right.'
'There was ... another more pressing and more embarrassing issue for us. We were actively searching for the WMD (weapons of mass destruction). We were sure we would find them. This was the moment I was waiting for ... It was, after all, the casus belli.'
'Of course, as I have said, the blunt and inescapable truth is that though Saddam definitely had WMD, since he used them, we never found them. The intelligence turned out to be wrong ... We admitted it. We apologised for it. We explained it, even.'
'The mistake is serious; but it is an error. Humans make errors. And, given Saddam's history, it was an understandable error.'
'So the aftermath was more bloody, more awful, more terrifying that anyone could have imagined. The perils we anticipated did not materialise. The peril we didn't materialised with a ferocity and evil that even now shocks the senses.'
On George W Bush
'George had immense simplicity in how he saw the world. Right or wrong, it led to decisive leadership.'
On Gordon Brown
'Political calculation, yes. Political feelings, no. Analytical intelligence, absolutely. Emotional intelligence, zero. Gordon is a strange guy.'
'So was he difficult, at times maddening? Yes. But he was also strong, capable and brilliant, and those were qualities for which I never lost respect.'
'It is true he is unsuited to the modern type of political scrutiny in which characters are minutely dissected. He was never comfortable as the 'normal bloke' sort of politician.'
On Bill Clinton
'We were political soulmates ... I was also convinced that his behaviour arose in part from his inordinate interest in and curiosity about people.'
On Boris Yeltsin
'The Russians were very weird to deal with at this time (the Kosovo crisis in 1999) ... By the time I knew him (Yeltsin), he had become, let us say, a bit unpredictable.
'I recall meeting him at an international summit shortly after the Kosovo conflict ... (He) came across the room to greet me with one of his famous hugs ... The hug began. The first ten seconds were, I thought, wonderfully friendly.
'The next ten began to get a little uncomfortable. The following ten started respiratory problems. I finally got released after about a minute and staggered off in search of a stiff drink. I think he made his point.'
On alcohol
'Stiff whisky or G&T before dinner, couple of glasses of wine or even half a bottle with it. So not excessively excessive. I had a limit. But I was aware that it had become a prop.'
