Blix told British Broadcasting Corp. radio that although there was a risk Saddam Hussein possessed weapons of mass destruction, the coalition should have allowed U.N. weapons inspections to continue for "a few months" longer.
"Do you go to war to any country where you say there is a possibility that they have weapons of mass destruction? No, I don't think it (military action) was at all obligatory," he told the BBC.
"I think they could have waited, they could have continued with inspections for a few months. We had been preparing ourselves for 2½ years and we only did 3½ months (of inspections)."
The United States and its allies Britain and Australia invaded Iraq in May after saying Saddam's regime was developing nuclear arms and likely possessed chemical and biological weapons. U.N. inspectors, who returned to Iraq in December, pulled out on March 18, two days before the United States and Britain launched the invasion.
However, a search by the U.S.-led Iraq Survey Group — made up of 1,400 scientists, military and intelligence experts — has failed to uncover any weapons of mass destruction since the conflict ended.
President Bush and British Prime Minister Tony Blair have come under increasing pressure to prove that Iraq had weapons of mass destruction.
"They over-interpreted," Blix said. "They were convinced that Saddam was going in this direction, and I think it's understandable against the background of the man that they did so, but you know, in the Middle Ages, when people were convinced there were witches, they certainly found them."
Blix criticized coalition calls for the Survey Group to be given more time to assess whether Saddam was developing illegal arms. "Now even in the past summer they said we must have some patience for the U.S. and U.K. investigations," he told the BBC. "So the patience they are requiring for themselves now was not anything that they wanted to give to us."
He accused the British government of falling prey to a "culture of spin, the culture of hyping…Advertisers will advertise a refrigerator in terms that we don't quite believe in, but we expect governments to be more serious and have more credibility."
In an interview with Australian radio broadcast Wednesday, Blix said he believed that Iraq had destroyed most of its weapons of mass destruction 10 years ago, but kept up the appearance that it had them to deter a military attack.
He added on Thursday that it was unlikely the U.S and British teams now searching for weapons in Iraq would find much.
"The U.S. and the U.K. have been there, they've had all the possibilities in the world to interview people who were not intimidated, and to go anywhere and they have not found any, so I think more and more…I'm leading to the conclusion that there aren't any," he said.
The U.S. "really intimated that we didn't see the whole story, but now it turns out what they had seen in large measure may not have existed," he said.