Evi Sachenbacher-Stehle has said that she is unable to explain how she could have failed a drug test at the ongoing 2014 Winter Olympics.

The German cross country skier and biathlete tested positive for methylhexanamine with A and B samples in Sochi.

"This is the worst nightmare you could imagine," BBC Sport quotes the 33-year-old as saying. "I can't explain how the doping test could be positive."

German Olympic Committee secretary-general Michael Vesper said: "We stand for a doping-free sport and a zero tolerance.

"We only want clean performances. Every doping case is initially a disappointment but also proof that the system works."

Italian bobsleigh brakeman William Frullani also tested positive for methylhexanamine with A and B samples and has been sent home.