LAUSANNE, Switzerland — A total of 31 athletes in six sports tested positive in reanalysis of their doping samples from the 2008 Beijing Summer Games, according to the International Olympic Committee.
The IOC said it opened disciplinary proceedings against the unidentified athletes from 12 countries.
The samples had been stored at the IOC laboratory in Lausanne. They were retested using enhanced methods on athletes who were expecting to compete at the Olympics in Rio de Janeiro in August.
The IOC said "all those athletes infringing anti-doping rules will be banned from competing" in Rio.
It added that the results of 250 retests from the 2012 London Olympics will "come shortly."
The committee will also undertake a "wider retesting" of medalists from Beijing and London.