The first athlete has been banned from the 2018 Winter Olympics for doping.
"I do understand athletes should not do any doping and even unintentionally".
The Court of Arbitration for Sport, CAS anti-doing division, which announced the discovery, lists the substance as a "diuretic or masking agent". "I do not want to be a disturbance to my teammates competing at the Olympic Games ... and will leave the team and the athlete's village voluntarily", he added. "I still can not fathom how his test results came back positive".
No results at the Pyeongchang Games have been affected as Saito is yet to compete.
"The athlete accepted, on a voluntary basis, to be provisionally suspended and to leave the Olympic Village", CAS said in a statement. "There's no merit or motive for me in using this medicine".
"Saito has no idea why this has happened, so we as Japanese Olympic team continue to make every effort to prove that there was no anti-rule violation by Kei Saito".
Tsutomu Kawasaki, Japan's short track coach, said the suspended Olympian "showed a lot of promise at a young age and has been educated on doping".
Japan has a relatively clean record when it comes to sports doping, but this case is the latest in a recent spate of infringements.
The IOC and anti-doping authorities have stepped up testing for the Winter Olympics following revelations of a Russian state sponsored doping plot at the last Games in Sochi, Russia.
In January, Yasuhiro Suzuki, a Tokyo Olympic hopeful in kayaking, spiked a fellow competitor's drink with an anabolic steroid and now faces a lifetime ban.
The 21-year-old has for the first time secured a spot on the Olympic team.
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