Russia’s Olympic Committee said Saturday that eight of its athletes from three sports at the 2012 Summer Games in London had tested positive for banned substances in a recent re-examination of their doping samples.

The announcement — posted to the Russian Olympic Committee website beneath a banner that read “Stop Doping” — came days after 14 Russian athletes from three sports were accused of having doped at the 2008 Summer Games in Beijing.

Ahead of this summer’s Olympics in Rio de Janeiro, the International Olympics Committee has reanalyzed roughly 700 samples from the past two Summer Games. It found a total of 55 drug positives, affecting athletes from at least 12 countries, that had previously gone undetected. Saturday’s announcement signaled that Russia’s athletes accounted for about 40 percent of them.

Last fall, a report published by the World Anti-Doping Agency accused Russia of a government-run doping program; as a result, the country’s track and field athletes were barred from international competition.