The Rio Olympics athletics programme suffered its first doping setback as Bulgarian runner Silvia Danekova has tested positive for EPO, sources told Reuters on Thursday.
Danekova, who raced the steeplechase at the 2012 London Olympics but did not get beyond the heats, used the banned blood booster erythropoietin (EPO).
Neither Danekova or her coach Rumen Angelov were immediately available for comment. The athletics programme begins on Friday.
"Unfortunately, we have a positive test," Bulgarian Olympic Committee's Secretary General Belcho Goranov told local media, refusing to name the athlete.
"We await the opening of the B sample test."
Sebastian Coe, president of the International Association of Athletics Federations, addressed the issue of doping on Wednesday, saying: "The last year has sorely tested all of us and all of our fans out there and our responsibility is to shape the future.
"So I genuinely hope that what they feel they're watching is our competitors doing it cleanly, and the vast majority are."
Danekova said she was ‘shocked’ by the result.
Danekova said the only logical explanation she could give for the positive test was that the substance came from a contaminated food supplement.
"I've been tested four times after entering the Olympic Village," Danekova, who faces a four-year ban if found guilty, told Bulgarian television on Friday.
"(Results) of the three of the samples were negative. It’s an incredibly big shock."
Danekova, who failed to get beyond the heats in the steeplechase at the 2012 London Olympics, said: "I don’t feel guilty. I cannot tell you how humiliated I feel.
"I feel robbed emotionally," she said. "But we’re coming from the east (eastern Europe), we’re too close to Russia ..."
Bulgarian athletics has been marred by a series of doping offences recently. Sprinters Tezdzhan Naimova and Inna Eftimova, middle-distance runners Daniela Yordanova, Vanya Stambolova and Teodora Kolarova, high jumper Venelina Veneva and hammer thrower Andrian Andreev have all tested positive in the last decade.
The country's weightlifting team were banned from Rio for repeated doping offences.
Image: Silvia Danekova of Bulgaria competes in the Women's 3000 metres steeplechase
Photograph: Christian Petersen/Getty Images for IAAF