Bulgarian steeplechaser Silvia Danekova and Chinese swimmer Chen Xinyi have tested positive for banned substances at the Rio Olympics.
The Bulgarian Olympic Committee (BOC) confirmed Danekova's positive test for banned blood booster EPO on Thursday and said Danekova had been temporarily suspended pending a test on her 'B' sample.
Danekova, 33, tested positive in a doping control conducted a few days after her arrival in Brazil on July 26.
She participated in the 3,000m steeplechase at London 2012 but failed to get past the heats.
"Unfortunately, we have a positive test," read a brief BOC statement.
Danekova has, however, denied taking performance-enhancing drugs and said she was shocked at the positive test.
"I've been tested four times after entering the Olympic Village," said Danekova, who faces a four-year ban if found guilty. "Results of the three of the samples were negative. It's an incredibly big shock.
"I don't feel guilty. I cannot tell you how humiliated I feel. I feel robbed emotionally. But we're coming from the East [eastern Europe], we're too close to Russia..."
Bulgaria are at the Games without a team in the weightlifting competition after a blanket ban for previous doping offences.
The Chinese Swimming Association later revealed Chen had become the first swimmer to test positive for banned substances in Rio after she failed a test for the diuretic hydrochlorothiazide
Hydrochlorothiazide, known as a masking agent, is a banned substance because it can be used to spur weight loss and cover up the presence of other illegal drugs by diluting urine collected in doping tests.
Chen, 18, finished fourth in the women's 100m butterfly on Sunday, missing a bronze medal by nine-hundredths of a second.
She was also scheduled for compete in the 50m freestyle which starts on Friday.