Iran, which Sunday had defeated Iraq 1-0 in the first leg in Arbil, suffered a 2-0 defeat against the team in the second leg on Thursday night.
“There are no excuses. Iran showed a bad performance against Iraq in Tehran’s Azadi Stadium and I am responsible for that,” Mansourian said.
Two goals by Amjad Radhi, one either side of halftime, put 2004 Athens Games semifinalists Iraq through to the third round of qualifiers.
“We were informed just before the match the Iraqi team was awarded a 3-0 victory in the first leg since one of the Iranian players should not have played as he has not been allowed to play,” Iran coach added.
Iran and Iraq have both qualified for the Olympics four times. Iran has not qualified for the Olympic since 1976.
Many of the 15,000 Iranian spectators walked out before the match ended. They shouted slogans against the head of the country's football federation Ali Kafashian, calling for his resignation.
Asia have 3.5 places at the 2012 Games, with the 12 winners of the second round clashes to be divided into three groups of four teams in the third round.
The three group winners will qualify while the three runners up will meet in next March for a three way tournament to decide who wins the right to face an African nation for a place in London.