The All-Russia Athletics Federation (ARAF) says four Russian track-and-field athletes have tested positive for the banned drug meldonium.
ARAF made the announcement on March 21, without naming the athletes.
But the TASS news agency quoted an unnamed source as saying the four included sprinter Nadezhda Kotlyarova, long-distance runners Andrei Minzhulin and Gulshat Fazletdinova, and steeplechaser Olga Vovk.
At least 16 Russian sportsmen and women, including world tennis star Maria Sharapova, have been caught using meldonium since it was added to the World Anti-Doping Agency's list of banned substances on January 1.
Russia was suspended from international track and field in the wake of a report last year exposing widespread cheating and corruption.
It now must provide evidence that it is fighting doping if it hopes to be reinstated and compete in the Rio Olympics in September.