That investigation is seeking to verify the account of Grigory Rodchenkov, Russia’s former antidoping lab director, who oversaw the Sochi lab. He told The New York Times that during Sochi he had worked at the direction of the Russian government, expunging the tainted urine of Russian athletes who were using performance-enhancing drugs. He said that with the help of the Russian intelligence service, he had gained access to supposedly tamper-proof drug sample bottles and had surreptitiously substituted in athletes’ clean urine.

Mr. Bach said the I.O.C. had no control over whether WADA’s investigation would be completed before the Summer Olympics in Rio de Janeiro, which start on Aug. 5. “This is in the hands of WADA,” he said, adding that he urged anyone with further information on the Sochi lab operation and Dr. Rodchenkov’s allegations to call an integrity and compliance hotline.

Dr. Rodchenkov’s account cast suspicion on not just the Russian athletes who competed in Sochi but those who competed at recent Summer Games, namely those in Beijing in 2008 and London in 2012.

According to Dr. Rodchenkov, director of the Moscow antidoping lab from 2005 to 2015, Russian athletes were doping in advance of Beijing and London. Before London, he said, he developed a three-drug cocktail of anabolic steroids that helped speed athletes’ recovery from grueling training regimens. Mixed with liquor, that concoction, he said, drastically decreased the drugs’ detection window, allowing athletes to dope days before competition.

On Tuesday, the I.O.C. announced that it had retested the doping samples of athletes who competed in Beijing, discovering 31 athletes from six sports and 12 countries with suspicious test results that could keep them from the Rio Games. Officials did not specify if Russia was included and said that further retesting of medalists’ samples from the London Games was planned and would be completed before the 2016 Olympics.