Millions of Swiss francs in bank accounts belonging to world soccer's governing body Fifa have been frozen, the Swiss justice ministry has said.
US officials believe "corruption money" may have been transited through the frozen accounts, the ministry said.
Between 50m and 100m Swiss francs ($50.1m-100.2m; £34m-£67m) has been frozen, media reports say.
Meanwhile, suspended Fifa President Sepp Blatter is appearing before the organisation's ethics committee
Mr Blatter, who is due to depart from Fifa on 26 February when his successor will be elected, arrived at the governing body's headquarters in Zurich in a chauffeur-driven car accompanied by one of his lawyers.
He is strongly pleading his innocence over corruption allegations being heard in front of the committee, made up of four judges. They are expected to make a ruling early next week.
The ethics investigation was launched following the decision by the Swiss attorney general to instigate criminal proceedings against Mr Blatter over a $2m (1.34m; €1.84m) payment to European soccer chief Michel Platini in 2011. Both men deny any wrongdoing.
Along with Mr Platini, Mr Blatter was suspended in October from participating in all soccer-related activity for 90 days pending a full inquiry into their conduct.
Some observers have highlighted the irony of Mr Blatter's appearance before the committee, given it was he who in 2012 gave it powers to become far tougher and more independent. He now argues that it does not have the power to remove an elected president and has complained of being the victim of an "inquisition".
The US is reported to have asked Switzerland to freeze about 50 accounts in 10 Swiss banks associated with its extensive inquiry into corruption in the highest echelons of world football, the Tages Anzeiger newspaper reported.
Correspondents say that if the committee rules against Mr Blatter, he could be banned from soccer for years.
Earlier this week, he used his own stationery to write to Fifa's 209 member state associations to proclaim his innocence.BBC