The International Olympic Committee has retested 454 anti-doping samples taken from athletes at the 2008 Beijing Olympics, with 31 competitors from six different sports and 12 countries failing tests.
The IOC said it had focused on athletes who were still active and therefore may have gone to the Rio Olympics this summer.
The Lausanne-based body's executive board announced that the results of 250 more re-tests from London 2012 would come shortly, with further retesting of medallists from 2008 and 2012 also planned.
