FIFA President Sepp Blatter has opened world football's congress - hours after refusing a request by UEFA to step down.
It is the first time he has been seen in public since the organisation he heads was mired in scandal after it was involved in two separate corruption investigations.
Mr Blatter said: "You will agree with me, these are unprecedented and difficult times for FIFA. They demand action and change from us all. It has to stop here and now.
"The events of yesterday have cast a long shadow over football and over this week's congress. Actions of individuals, if proven, bring shame and humiliation on football, and demand action and change from us all.
"We cannot allow the reputation of football and FIFA to be dragged through the mud any longer. It has to stop here and now.
"I know many people hold me ultimately responsible for the actions and reputation of the global football community, whether it is a decision for the hosting of a World Cup or a corruption scandal.
"We, or I, cannot monitor everyone all of the time. But it must fall to me to bear the responsibility for the reputation and wellbeing of our organisation, and find a way to fix things."
During a defiant speech, he said the scandal-tainted football body faced "more bad news" and that the next few months would "not be easy for FIFA", but said that "we" now had to earn back "trust".
He ended by asking everyone to remember that those involved football were not there "for greed... for exploitation... for power, but because of love for the game".
Mr Blatter was speaking after saying he intends to run for President for a fifth term despite a call by UEFA head Michel Platini for him to quit.
The European football body decided it would not boycott the congress but is supporting Mr Blatter's opponent Prince Ali bin al Hussein of Jordan in the presidential race.
The vote for president takes place on Friday.
Mr Blatter opened the congress after Swiss police confirmed they will be questioning 10 FIFA executives over the decision to award World Cups to Russia and Qatar, and sponsors expressed serious concerns over a corruption scandal engulfing the governing body.
The move came after separate from US allegations of a $150m bribery racket stretching back 24 years, which saw seven senior FIFA officials arrested in an early morning raid on their five-star hotel in Zurich on Wednesday.
After he finished speaking, he received a round of applause from the delegates who come from all 210 countries that make up world football's governing body.
The British member of FIFA's executive committee, former Manchester United CEO David Gill, said he would resign for the body, where he is a Vice President, if Mr Blatter is re-elected.
As Mr Blatter arrived at the Zurich venue where the congress is being held, he refused to answer questions about whether he would postpone the vote or would step down.
He had earlier missed three public appearances and been forced to chair a crisis meeting of world football leaders from FIFA's six regions.
Mr Platini said he had held the private conversation with Mr Blatter because he regarded him as a friend but had urged Mr Blatter to step down because he was giving FIFA a "terrible image".
He said the FIFA President had told him he could not stand down because the congress was about to start.
Mr Platini said: "I was very clear, I told him that I would have liked to have told him this among the two of us.
"I'm saying this with sadness and tears in my eyes, but there have been too many scandals, FIFA doesn't deserve to be treated that way."
David Cameron has said he welcomes the investigation in world football's controlling body, tweeting: "I welcome the probe into allegations of FIFA corruption and bribery, and support the FA's call for new leadership and reform."
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