Bulgaria's Silvia Danekova has become the first athlete at Rio 2016 to test positive for a banned substance in an in-competition doping test.
According to Reuters, the 33-year-old has been temporarily suspended pending the test of her B sample. She tested positive for the banned substance in a doping control held just days after her arrival in Rio on 26 July.
Danekova was due to represent her country in the women's 3000m steeplechase.
Reuters add Danekova has tested positive for erythropoietin, a substance used to illicitly boost an athlete's red blood-cell supply.
"Unfortunately, we have a positive test," Bulgarian Olympic Committee's Secretary General Belcho Goranov said. "We expect the opening of the B sample test."
In November 2015, Bulgaria's weight lifting team were banned from this summer's Olympics due to wide spread cases of doping.
The build-up to Rio 2016 was dominated by the doping scandal that has seen 267 Russian athletes across 18 sports banned from competition following reports of "state-sponsored" doping operation in Russia.
Russian athletes have also since been banned from competing at the Rio 2016 Paralympics.