Saito, 21, failed an out-of-competition test prior to the event, the anti-doping authority said in a statement, adding that he tested positive for acetalozamide, a banned diuretic which is considered as a masking agent.

The CAS statement said Saito had left the athletes' Olympic Village voluntarily and would be provisionally suspended from the Olympics and other competitions pending a full investigation.

Sato, a human biology student whose sister Hitomi is also competing in Pyeongchang, was a member of Japan's 3,000m relay team that finished third at the 2013 and 2014 world junior championships.

He competed on Saturday in the short track speed skating 1,500 metres but was eliminated in the heats. He was scheduled for more races during the Games.