Russian 400-metre runner Nadezhda Kotlyarova has tested positive for the banned substance meldonium.
Kotlyarova told Russia's Tass agency she failed a drug test at last month's Russian indoor championships and is protesting her innocence.
She claimed the spate of positive tests for the endurance-boosting meldonium, which was added to the banned list from January 1, is an injustice.
The 26-year-old Kotlyarova raced at last year's world championships in Beijing, reaching the semi-finals, and was also part of the Russian relay team which won silver in the 4x400m at the 2013 European indoor championships.
She was not racing in this week's world indoor championships in Portland because Russia was suspended from global track and field in November over doping.
Russians make up more than half of the more than 20 meldonium doping cases identified so far, with Maria Sharapova the best-known athlete to have been suspended.
On Friday, the World Anti-Doping Agency said there had been 102 failed tests for meldonium this year, though only a small fraction of athletes' names have so far been made public.
The IAAF did not respond to a request for comment on Kotlyarova's case.
If confirmed to involve meldonium, it would be the third such case in track and field worldwide after former world 1500m champion Abeba Aregawi of Sweden and the former European indoor 800m champion Nataliya Lupu of Ukraine.
Share
