Zurich - Joseph Blatter's 17-year tenure at the head of FIFA is to come to an end after he announced late on Tuesday he would resign as head of football's world governing body amid corruption probes, saying FIFA needs "a profound overhaul."
Blatter called for an extraordinary congress to elect his successor.
"I will organize an extraordinary congress for a replacement for me as president," he said at a hastily convened press conference in Zurich.
"I will not stand. I am now free from the constraints of an election. I will be in a position to focus on profound reforms. For many years we have called for reforms. But these are not sufficient. FIFA needs a profound overhaul."
Blatter's decision will end 17 years in charge of FIFA and comes four days after the 79-year-old Swiss was elected for a fifth four-year term as head of football's world governing body.
Blatter will carry out his functions as FIFA president until a successor is elected. He said there would be significant reforms to be led by Domenico Scala, chairman of FIFA's audit and compliance committee.
"FIFA's interest are dear to me. That's why I have taken this decision. What counts most for me is the institution of FIFA and football around the world," he said.
"While I have a mandate from the membership of FIFA, I do not feel that I have a mandate from the entire world of football - the fans, the players, the clubs, the people who live, breathe and love football as much as we all do at FIFA. Therefore, I have decided to lay down my mandate at an extraordinary elective congress."
The decision came on a day when it emerged that US authorities investigating corruption believe FIFA secretary general Jerome Valcke was the top FIFA official behind a payment of 10 million dollars to accounts controlled by a former FIFA vice-president Jack Warner of Trinidad and Tobago, who is now under criminal investigation.
Authorities are investigating the transfer of the sum, paid by FIFA on behalf of 2010 World Cup hosts South Africa, which had been unable to pay directly from government funds.
US-based ABC News, citing sources familiar with the case, said Tuesday that Blatter himself was target of the probe. One source was quoted as saying that "people are going to want to save themselves" and that means "there's probably a race to see who will flip on (Blatter) first" - meaning to inform on co-conspirators.
The US Justice Department decline to comment on the report, in response to a dpa inquiry.
At the Zurich press conference, Scala said that based on FIFA statutes a four-month notice is required for any presidential elections to be held.
FIFA needed time to vet potential candidates and for the candidates to present their "vision" for FIFA, with the timing likely between December and March, he said.
"FIFA is determined to address the issues that are afflicting FIFA," Scala said. "We want to fundamentally reform the way in which people see FIFA."
In a first reaction, UEFA president Michel Platini, seen as a possible Blatter successor, called the announcement "a difficult decision, a brave decision, the right decision."
Prince Ali Bin Al Hussein of Jordan, who lost to Blatter in Friday's presidential election, told CNN: "I think that it is the right move from Sepp Blatter, and I think we have to look to the future."
Prince Ali declined to say if he would run again but was "at the disposal" of all the national associations who want a change.
England's FA chief Greg Dyke said: "We welcome today's announcement and believe it is good news for world football and FIFA. Change at the very top of FIFA is the necessary first step in delivering real reform of the organization."
FIFA was moved to explain the 10-million-dollar payment to accounts held by Warner, part of the US investigation and indictments issued last week.
Warner, former head of the Central and North American confederation CONCACAF, was one of 14 people indicted in the United States last week on bribery and corruption charges.
He is alleged to have taken a bribe in exchange for helping South Africa secure the right to host the 2010 World Cup.
FIFA said the 10 million dollars were paid to Warner following a request by the South African government to "support the African diaspora in Caribbean countries as part of the World Cup legacy," and was asked by the country's football association SAFA "to process the project's funding" by withholding the 10 million dollars from the South Africa World Cup operational budget.
"SAFA instructed FIFA that the Diaspora Legacy Programme should be administered and implemented directly by the president of CONCACAF (Warner)" to act as trustee for the Diaspora Legacy Programme Fund.
"Neither the Secretary General Jerome Valcke nor any other member of FIFA's senior management were involved in the initiation, approval and implementation of the above project," the statement said.
FIFA said the 10 million dollars were authorized by the then-chairman of the finance committee, the late Julio Grondona, and "executed in accordance with the organization regulations of FIFA."
Warner is facing extradition to the United States on bribery and racketeering charges as 14 present and former football officials and corporate executives have been charged by the US justice department in connection with bribery, corruption and money laundering.
Seven senior football officials were arrested in dawn raids at a Zurich hotel Wednesday ahead of the FIFA congress.
There is a separate Swiss investigation on the 2018 and 2022 World Cup vote won by Russia and Qatar. Swiss prosecutors said Blatter's resignation would not affect the Swiss probe into those votes.
The United States denied it had sought to push out Blatter after last week's US indictments.
"No, the United States government does not have a position on who the president of FIFA is," State Department spokeswoman Marie Harf said.