Swiss banks reported suspicious activity around accounts of football’s world governing body Fifa, says the Swiss attorney general.
Michael Lauber said his office was analysing a “huge amount” of seized Fifa data in its corruption inquiry.
He said he did not rule out interviews with Fifa president Sepp Blatter as part of his investigation.
The inquiry surrounds possible criminal activity in the bidding process for the 2018 and 2022 World Cups.
Leading Fifa official Domenico Scala has said Russia and Qatar could lose those tournaments if evidence emerges of bribery.
Both countries deny any wrongdoing.
Fifa is facing claims of widespread corruption after Swiss police raided a hotel in Zurich – where Fifa is based – and arrested seven of its top executives last month.
The seven were held at the request of the US department of justice, which has charged 14 current and former Fifa officials and associates on charges of “rampant, systemic, and deep-rooted” corruption.
The charges follow a major inquiry by the FBI.
Until now, much less has been revealed about the Swiss investigation than the inquiry being led by the FBI.
Mr Lauber told a news conference that his investigation was looking at 53 banking relationships reported by the Swiss financial intelligence unit.
“We are facing a complex investigation with many international implications. The prosecution is ongoing and will take time. The world of football needs to be patient – by its nature, this investigation will take more than the legendary ’90 minutes’,” he said.