Switzerland's investigation targeting the bidding process for the 2018 and 2022 World Cups began in May, after the US justice department unsealed charges against 14 people accused of massive graft at world football's embattled governing body.
Swiss investigators have searched houses, confiscated masses of electronic data, and scrutinized 121 bank accounts, Switzerland's Attorney General Michael Lauber told reporters, speaking alongside his US counterpart Loretta Lynch.
He said his investigation “is not even near the half-time break”.
“Financial assets have been seized, including real estate, for example flats in the Swiss Alps,” Lauber said, although he has not named any individuals who could ultimately be subject to criminal charges.
Fifa officials have previously said it was possible that Russia and Qatar — awarded the 2018 and 2022 World Cups respectively — could be stripped of their hosting rights if there was clear evidence of bribery in the bidding process.
Lynch's case — which includes charges against nine ex-Fifa officials and five sports marketing executives — is separate from the Swiss probe, although she underscored that the two countries have cooperated throughout.
The top US prosecutor said that she anticipates “pursuing additional charges against individuals and entities,” but refused to comment on whether an indictment was possible against Fifa President Sepp Blatter.
“The scope of our investigation is not limited, and we are following the evidence where it leads,” Lynch further said, adding that the inquiry had “expanded since May”.
The 79-year-old Blatter has announced that he will step down when his successor is chosen at a special election in February, but he has fiercely denied any wrongdoing, blaming all impropriety under his watch on “rogue” individuals.
Of the seven people arrested in Zurich in May in connection with US charges, only one, ex-Fifa vice president Jeffrey Webb of the Cayman Islands, has been extradicted to face trial in American courts.
Swiss justice officials have said they are likely to rule on the remaining six extradition requests this month.
Lynch said she was “hopeful” that all would be sent to the US.
The top US prosecutor has said she has uncovered decades of bribery worth more than $150 million at world football dating back to 1991.
She said her investigation, which has relied on cooperation from multiple countries, aims to permanently eliminate the culture of graft that has plagued the world's most popular sport.
“To anyone who seeks to live in the past and to return soccer to the days of corruption and bribery, cronyism and patronage, this global response sends a clear message: you are on the wrong side of progress,” Lynch told reporters.