Russia has been stripped of a silver medal it won at the 2012 London Olympics after new tests on a sprinter detected banned substances.
Antonina Krivoshapka, 29, took silver as part of the Russian 4 x 400 metre relay team and had passed drugs tests at the time.
However, the International Olympic Committee says "improved analytical methods" have now detected the banned steroid turinabol in samples the athlete she submitted.
Two other athletes have also been disqualified from the event after retrospectively failing anti-doping tests.
Turkish boxer Adem Kilicci and Russian discus thrower Vera Ganeeva's samples from the event have now tested positive for the steroid, the IOC confirmed.
This IOC's decision comes into force immediately and Russia has been asked to return the silver medal "as soon as possible."