By Simon Evans and Joshua Franklin
ZURICH (Reuters) - World soccer chief Sepp Blatter and European boss Michel Platini were both suspended on Thursday in an ever-deepening corruption scandal, decapitating the leadership of the sport as it faces criminal investigations on both sides of the Atlantic.
Blatter, the Swiss who has been president of world governing body FIFA since 1998, was already due to stand down after an election for his replacement in February.
But Platini, head of European body UEFA, was a frontrunner to replace him and his shrinking election hopes now depend on whether he can overturn the 90-day ban imposed by FIFA's Ethics Committee.
"During this time, the above individuals are banned from all football activities on a national and international level," the committee said in a statement.
FIFA said Blatter was not allowed to represent it in any capacity, and his acting replacement would be Issa Hayatou of Cameroon.
FIFA also handed out a 90-day suspension to Secretary General Jerome Valcke, who had already been sent on leave after being accused of being part of a scheme to sell 2014 World Cup tickets at a marked-up price.
All three officials have denied any wrongdoing.
South Korea's former FIFA Vice-President Chung Mong-joon was banned from the game for six years, a decision which will almost certainly end his already slim electoral hopes.
Swiss and U.S. authorities are both investigating corruption in world soccer, in long-running probes that burst into public view with dawn raids on a Swiss hotel in May and the indictment of 14 soccer officials and sports marketing executives.
Among other things, they are examining the awarding of the 2018 and 2022 World Cups to Russia and Qatar respectively.
All those banned on Thursday can turn to FIFA's Appeals Committee to try to overturn the bans, but would remain suspended throughout any appeals process.
Blatter's lawyers said he was disappointed he had been suspended without having the chance to be heard. They added he was looking forward to presenting evidence that would prove he did not engage in any misconduct.
Platini, a former France midfield star, said he submitted his nomination papers for the election to succeed Blatter before he was suspended. Shortly before his ban was announced, he indicated he intended to fight against the ruling.
"I will stop at nothing to ensure that the truth is known," Platini said in a statement. "Nobody should be in any doubt as to my determination to achieve that objective."
"In the meantime, a dispassionate, independent and impartial judicial body needs to shine a light on the events that led the FIFA Ethics Committee to open these investigatory proceedings," added the Frenchman.
A spokesman for Platini was unable to comment on whether he intended to appeal.
If Platini is not able to overturn his ban and get into the election race, it would leave Prince Ali Bin Al Hussein of Jordan as the clear favorite, unless other candidates now emerge to take advantage of Platini's woes.
The statement from the Ethics Committee did not give out details of any offence committed by Blatter and Platini.
While it is not allowed to discuss any probes, the investigation is almost certainly looking into a 2 million Swiss francs payment from FIFA to Platini in 2011, nine years after he completed a spell working for Blatter as an adviser.
The Swiss Attorney General said on Sept. 25 it had opened a criminal investigation into Blatter concerning that matter and a Caribbean television rights deal. Platini is regarded as somewhere "between a witness and an accused person" in the payment case.
Blatter has worked for FIFA for 40 years, starting as a technical director before becoming secretary general under former president Joao Havelange in 1981.
The 79-year-old Swiss told a German magazine this week that the Swiss criminal investigation against him was "not correct".
(Reporting by Joshua Franklin and Simon Evans; Editing by Mark Trevelyan)