The FBI and federal prosecutors are investigating allegations of widespread doping by Russian athletes, a U.S. law enforcement official told CNN on Tuesday.
The probe is more than a year old, meaning it predates media reports from November 2015 that alleged massive cheating by Russian athletes.
The U.S. attorney's office for the Eastern District of New York is taking on the case, the New York Times reported Wednesday.
It is the same office that handled indictments against officials in FIFA, soccer's international governing body.
The emergence of a federal investigation, however, elevates scrutiny of Russian athletes just ahead of the Rio Olympic Games, which open in the Brazilian city on August 5.