Former British Prime Minister Tony Blair was on the front foot Friday justifying his reasons for dragging Britain into the controversial Iraq War.

Blair appeared for most of the day at the UK inquiry into the war. He made clear at the outset that the attacks of September 11 2001 in the United States, prompted him to join U.S. efforts to invade Iraq. Until then he said he believed sanctions could work, but just as likely wouldn't.

After September 11, even in the early days following the attacks, he was in deep discussions with the United States about invading Iraq.

"After September 11 what changed, as I say, was our calculation, mine and I think the Americans' as well, was that we couldn't go on like this," he said.

Blair said there were 24 cabinet meetings prior to the Iraq invasion, however he conceded the "options paper," a document drawn up to deal with Iraq was discussed outside cabinet, and not at Downing Street but at Chequers. He also conceded the options paper did not go to all members of cabinet. Clare Short, a minister in the Blair government at the time who resigned over the decision to invade Iraq, was one minister who did not receive the paper. The options paper outlined the impact of sanctions versus UN weapons inspections versus removing Saddam Hussein from power.

"The primary consideration for me was to send an absolutely powerful, clear and unremitting message that, after September 11, if you were a regime engaged in WMD, you had to stop," Blair told the inquiry.

The former British prime minister conceded under questioning the threat of Saddam Hussein, or of Iraq possessing weapons of mass destruction, had not been changed by the events of September 11, but that the perception of risk had changed.

"Now, my assessment of risk prior to September 11 was that Saddam was a menace, that he was a threat, he was a monster, but we would have to try and make best," he said.

"If you had asked me prior to September 11, did I have any real belief in his good faith. No, I didn't. Did I really think that a new sanctions framework was going to do the trick? No, I didn't. On the other hand, precisely because the consequence of military action is so great, for me the calculus of risk was, "Look, we are just going to have to do the best we can". After September 11, that changed, and that change, incidentally, I still believe is important for us today because it is the reason today, as I say, I do take such a strong line on Iran or any other nation that tries to develop WMD."

"We cannot afford, in my view look, other people may have different views, but in my view, we cannot afford the possibility that nations, particularly nations that are brutal, rogue states, states that take an attitude that is wholly contrary to our way of life, you cannot afford such states to be allowed to develop or proliferate WMD," the former British prime minister told the inquiry.

Mr. Blair said the regime of the late Iraqi leader Saddam Hussein was "appalling" and that "we couldn't risk" such a regime developing weapons of mass destruction.

Tony Blair was prime minister in 2003 when he joined forces with former U.S. President George W. Bush to lead the Iraq invasion.

Both leaders firmly claim they believed the late Iraqi leader Saddam Hussein had weapons of mass destruction. The weapons were never found and many critics are questioning whether the war was legal.

Mr. Blair told the inquiry that the only commitment he made in talks with Mr. Bush was "a commitment to deal with Saddam."

The former prime minister's decision to send thousands of British troops to Iraq was one of the most controversial of his time in office, provoking accusations he had deceived the public about the justification for war.

An audience seated in a London convention center for the inquiry included family members of soldiers and civilians killed or missing in Iraq.

Mr. Blair arrived at the inquiry early and entered through a rear entrance, dodging protesters in the front of the building.

The former prime minister has appeared at previous inquiries, but Friday's appearance is the first time he has been questioned with the public watching.