An investigation by the authorities in Switzerland into the activities of FIFA, world soccer’s governing body, will include the examination of more than 50 suspicious financial relationships, the country’s chief federal prosecutor said on Wednesday.

Michael Lauber, the official leading the investigation, said at a news conference that his office had received 53 reports involving FIFA from banks concerned about transactions, adding that his team had “obtained evidence concerning 104 banking relations.”

He added, “And be aware that every banking relation represents several bank accounts.”

Mr. Lauber also said it was possible that his office would seek to interview top FIFA officials such as Sepp Blatter, the longtime president who has announced he will resign, and Jérôme Valcke, Mr. Blatter’s top deputy, who has been linked to a $10 million payment that American law enforcement officials suspect of being a bribe.

Speaking in Bern, Switzerland, after being re-elected for another four-year term as Switzerland’s attorney general, Mr. Lauber said that Swiss officials had seized about nine terabytes of digital evidence during a sweep of FIFA’s offices in Zurich.