Swiss prosecutors are investigating 53 cases of possible money laundering as they look into FIFA’s handling of bids for the 2018 and 2022 World Cup bids, officials said on Wednesday.

Attorney general Michael Lauber said the “suspicious” transactions had been reported by banks and that a “huge and complex” inquiry into football’s world body could take months if not years.

“We note positively that banks in Switzerland did fulfil their duties to file suspicious activity reports,” he told a press conference.

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“Partly in addition to the 104 banking relations already known to the authorities, banks announced 53 suspicious banking relations via the Anti-Money-Laundering-Framework of Switzerland,” he added.

The Swiss inquiry into the World Cup bids – which went to Russia for 2018 and Qatar in 2022 – is one of two major fraud investigations that have rocked FIFA.

US authorities last month charged 14 people in a separate bribery investigation.

Lauber said he “does not exclude” questioning FIFA boss Sepp Blatter or general secretary Jerome Valcke, although neither is currently under suspicion.

Sepp Blatter announced he would step down as FIFA boss.

He said nine terrabytes of data had been seized, including at FIFA’s Zurich headquarters and the probe would take time.

“The world of football needs to be patient … by its nature, this investigation will take more than the legendary ’90 minutes’,” said Lauber, who has just been re-elected for a four-year mandate.

Lauber said he did not feel under pressure with the next World Cup in Russia just three years away.

“I don’t care about the timetable of FIFA, I care about my timetable,” he said in response to a question.

Senior FIFA official Domenico Scala has said there could be a re-vote for the 2018 and 2022 World Cups if there was evidence of wrongdoing in the bidding process.

FIFA, never far from controversy, is facing its biggest crisis because of the two corruption inquiries. Four days after being elected to a fifth term on May 30, Blatter announced that he would resign.

Seven FIFA officials were detained at a luxury Zurich hotel as part the inquiry on May 27. They are now fighting extradition to the United States.

On Thursday, the European parliament called on Blatter to quit immediately and allow for an interim leader to launch reforms in the organisation.

But FIFA has repeated that the 79-year-old Swiss will continue in office until a successor is designated, probably by the end of the year.

The FIFA Executive Committee will meet in Zurich on July 20 to fix a date for the congress to elect Blatter’s successor.

The vote will not be before December.