Moscow - Russian curler Alexander Krushelnitsky tested positive for the banned substance meldonium at the Pyeongchang Olympics, the Russian Olympic Committee (ROC) confirmed on Tuesday.
"The (B) sample gave a positive result, confirming the presence of a banned substance in the body," the ROC said in a statement.
"We deeply regret this incident," the committee said.
But it said the concentration of meldonium was "absolutely insignificant from the point of view of any sort of therapeutic effect on the human body," adding that Krushelnitsky's previous tests had come back negative.
The ROC said it would begin a comprehensive investigation into the case.
"We completely share and support the IOC and WADA position of zero tolerance for doping and will take all necessary measures to ensure guilty parties are punished to the fullest extent," the statement added.
Krushelnitsky passed rigorous vetting to attend the Pyeongchang Olympics, raising questions over the testing programme and the move to let Russians compete despite systemic doping.
Krushelnitsky, who won bronze in the mixed doubles curling with his wife Anastasia Bryzgalova, was one of 168 athletes passed as "clean" and allowed to compete as neutrals after a targeted testing programme stretching back over several months.
Russian curling federation president Dmitry Svishchev earlier dismissed the case against Krushelnitsky as a "provocation, a subversive act".
Svishchev said the federation did not recognise that Krushelnitsky took the banned substances voluntarily, in comments carried by Russian news agencies Tuesday.
Russia were banned as a team from the Olympics in December after investigations revealed an extensive doping plot culminating at the Sochi 2014 Winter Games, where the hosts topped the medals table.