A gymnast from Uzbekistan has been provisionally suspended from the London Olympics after testing positive for a diuretic.
Luiza Galiulina, 20, gave a urine sample five days ago that came back positive for the prohibited substance furosemide.
Galiulina claimed that she "did not know" how the substance came to be in her body but that she had been treated by her mother when she was sick at the end of June, and was also taking medication for a heart condition, the International Olympic Committee (IOC) said.
A definitive decision on her fate will be decided after the B sample is analysed.
Like some other diuretics, furosemide is listed on the World Anti-Doping Agency's banned drugs list as it can be used as a masking agent to disguise the use of other drugs. It is also often used by athletes seeking to lose weight.
Furosemide is deemed "a specified substance" on the WADA list, which means that if a person can prove that it was taken by accident, the usual two-year ban for doping offences can be downgraded to a warning.
Galiulina was due to compete in the qualifying session at Greenwich on Sunday night.
It is the second case of doping at the Olympics, after Albanian weightlifter Hysen Pulaku tested positive for a banned steroid and was banned immediately.
More than a dozen other athletes have already been expelled for pre-competition doping offences, but Pulaku, 19, was the first to fail a test since arriving for the Games.
Among the pre-Games doping casualties were Morocco's Mariem Alaoui Selsouli, one of the favourites for the women's athletics 1500m gold medal, who failed a test for a banned diuretic.
World anti-doping chiefs have unveiled a new test for human growth hormone, with a detection window of weeks rather than hours, which they hope will snare drug cheats at the Games.
A total of 15 athletes were caught doping at the 2008 Beijing Olympics, the most at a Summer Games since the IOC began testing at the 1968 edition in Mexico City.
- with AFP