A Chinese swimmer and a Bulgarian runner have both failed doping tests at the Rio Olympics.
Women's swimmer Chen Xinyi, 18, tested positive for the banned substance diuretic hydrochlorothiazide, China's Xinhua agency reported.
It came hours after steeplechase competitor Silvia Danekova, 33, was suspended after she also failed a test at the games.
The two women are the first athletes to fail tests inside an Olympics race that has been foreshadowed by controversies around doping.
Danekova has vigorously denied taking performance-enhancing drugs and said she was shocked at testing positive for the banned substance erythropoietin (EPO) a few days after her arrival in Brazil.
She was due to compete in the women's 3000m steeplechase on Monday but has been suspended pending the result of her test on her 'B' sample.
The runner suggested that she may have tested positive as the result of a contaminated food supplement.
"I feel robbed emotionally," she said, adding that she may have suffered as her nation is seen as "too close" to Russia.
Russia has seen almost all its track and field team barred from this year's Games over a doping scandal.
Meanwhile Chen has applied to the the International Olympic Committee for a hearing to look into her case after she tested positive, Xinhua cited the Chinese Swimming Association (CSA) as saying.
The swimmer had finished fourth in the women's 100m butterfly final on Sunday, and was scheduled to swim in the 50 freestyle heats on Friday in Rio.
Leading Olympic nation China has said it holds a zero-tolerance approach to doping and had taken "all necessary measures" to ensure that its athletes are clean.
"The Chinese Swimming Association resolutely opposes the use of banned substances, will actively cooperate with the investigation by the Court of Arbitration for Sport, and respect its final ruling," an official said.
Controversies over doping overshadowed the build-up to Rio and, far from dying down as events got under way, have flared anew as US and Australian competitors have branded their Russian and Chinese rivals as drug cheats.