Four Russian track-and-field athletes have tested positive for the banned drug meldonium, Russia’s athletics chief said yesterday, a disclosure that further undermines Moscow’s efforts to overturn a doping ban in time for Rio.

At least 16 Russian sportsmen and women, including world tennis star Maria Sharapova and speed skating Olympic gold-medallist Semion Elistratov, have been caught using meldonium since it was banned by the World Anti-Doping Agency on January 1.

Despite warnings from sports officials that a number of other Russian competitors could have taken the substance, Sports Minister Vitaly Mutko told Reuters on March 11 that meldonium had nothing to do with athletics in his country.

But Dmitry Shlyakhtin, head of the Russian Athletics Federation (ARAF), said yesterday four athletes had now tested positive.

“We have information that four people gave positive tests for meldonium,” the Interfax news agency quoted him as saying.

Shlyakhtin did not name the athletes and it was unclear whether Russian sprinter Nadezhda Kotlyarova, who revealed on Sunday she had taken meldonium, was included as one of the four.

The scandal will complicate Russia’s campaign to prove it is compliant with anti-doping standards after being suspended from international competition last year following revelations of widespread cheating and corruption.

If it cannot get the suspension lifted, Russian athletes will miss the Olympics starting in Rio de Janeiro on Aug. 5 – a humiliating blow to a country that has long drawn pride and prestige from its record as an athletics superpower.

Mutko said the cases of meldonium use in Russian sport should not be connected to his country’s preparations for the Olympics, and athletes would be tested three times before leaving for Rio.