Chinese swimmer Chen Xinyi and Bulgarian steeplechaser Silvia Danekova have tested positive for banned substances in the first failed doping tests at the Rio Olympics.
The 18-year-old female swimmer failed a doping test in Rio de Janeiro on August 7, the Chinese news agency Xinhua reported, citing the Chinese Swimming Association.
The swimmer has asked for an examination of the B sample.
Further details about the doping investigation were not immediately known. International Olympic Committee spokesman Mark Adams said on Friday that his organization would not comment until the Court of Arbitration for Sport, which is for the first time independently handling doping cases, completes its procedure.
"We will not comment on any name of any athlete, any sport, any national Olympic committee until the procedure is over and the decision has been communicated, which for reasons of justice is I think the correct decision," Adams told journalists in Rio.
Chen Xinyi finished fourth in the 100-metre butterfly on Sunday and was scheduled to compete in the 50-metre freestyle on Saturday.
The Bulgarian Olympic Committee confirmed Friday that both the A and B samples of a doping probe on Danekova were positive.
The 33-year-old was tested on July 30 immediately upon her arrival in the Olympic Village and was found positive for the performance boosting eryrhropoiesis-stimulating agent (ESA), which stimulates red blood cell production.
Danekova, who was due to compete in Saturday's 3,000m steeplechase heats, has been suspended.
She told Bulgarian broadcaster bTV she would now end her athletic career.
Bulgaria's sports ministry condemned Danekova, saying in a statement: "It is inadmissible that the image of Bulgaria is destroyed in this way and a stain placed on the entire Bulgarian sport."
Nearly 2,400 doping tests have been conducted at the Rio Olympics so far, Adams said, comprising 2,033 urine tests, 130 blood tests and 232 biological passport controls.
It is planned to carry out some 5,500 doping tests of the more than 11,000 athletes taking part in the Games, which run until August 21.