Results from the second wave of retesting further tainted the results of those competitions, bringing the total number of implicated athletes to 98. The new results affected 30 athletes from eight countries who competed in four sports in Beijing, and 15 athletes from nine countries who competed in two sports in London, according to the I.O.C.
The I.O.C. said it could not immediately identify the implicated athletes or countries for legal reasons and that it was in the process of informing the individuals — 23 of whom won medals in Beijing — along with their national Olympic committees and relevant sports federations.
“The new reanalysis once again shows the commitment of the I.O.C. in the fight against doping,” Thomas Bach, president of the committee, said in a statement on Friday.
Last month, as concern about systematic doping mounted, Mr. Bach called the antidoping system deficient and ordered a sweeping re-examination of its structure after this Summer’s Games.
Richard W. Pound, a former head of the World Anti-Doping Agency, said Friday that it was natural for science to improve over the years, revealing more doping offenses.
“The system is actually pretty good,” Mr. Pound said. “It’s the people sitting around the table that don’t want it to work.”
In Friday’s announcement, the I.O.C. said that retests of past doping samples — which the committee has the authority to conduct up to 10 years after they were collected — would continue in two more rounds, to be carried out during and after the Rio Games, which start Aug. 5.
The retesting results released in May focused on past Olympians with a chance at competing in Rio, the I.O.C. said. The second round of results released on Friday paid specific attention to medalists.
The relevant urine samples of athletes dating to the 2008 Games are stored in the freezer of a laboratory in Lausanne, Switzerland. In its announcement, the I.O.C. said it had used “the very latest scientific analysis methods.”
Still, in a cat-and-mouse dynamic, both testing methods and doping methods have gotten more sophisticated, with those seeking to beat the system devising new ways to skirt detection.
Don Catlin, a former head of the Olympic Analytical Lab at U.C.L.A., said he was not surprised that new violations had been uncovered, but he called the 98 positives a high figure.
Mr. Catlin, who was present at both the London and Beijing Olympic labs, praised the performance of both facilities.
“There was a tremendous amount of equipment, very well-trained staff. They were not about to miss anything,” he said of the London lab. “But always, as time goes on, new methods are going to be more sensitive and yield more positives. You’d have to expect a few.”
Grigory Rodchenkov, Russia’s longtime antidoping lab director, told The New York Times in May that he had divined a way to speed up athletes’ absorption of banned substances, decreasing the likelihood that they would be caught. His method was to mix drugs with liquor, he said, and to have Russia’s top athletes swish the concoction, known as the Duchess cocktail, under the tongue to accelerate the body’s processing of the drugs.
Russian officials have broadly denied those specific allegations, though this week, President Vladimir V. Putin announced provisional suspensions of sports officials accused of being involved in the elaborate doping schemes.
In Moscow on Friday, Mr. Putin announced the creation of an antidoping commission that would consist of Russian and international experts, jurists and public figures. The announcement came two days before Olympic officials were expected to deliberate for the final time on whether to bar Russia’s national team ahead of the Rio Games, as antidoping advocates have requested, or to defer to specific sports federations.
Mr. Putin said Russia’s longest-serving member of the I.O.C., Vitaly G. Smirnov, would lead Russia’s new commission. The new body will develop a national plan to combat doping in Russian sports and monitor its execution, he said.
The face of Russia’s antidoping efforts amid scandal in recent months had been Natalia Zhelanova, the antidoping adviser to Russia’s sports minister. But this week, Ms. Zhelanova, too, was implicated, after an investigation commissioned by WADA found that she had been a key liaison in helping to cover up drug violations.
In an interview last week, Ms. Zhelanova denied involvement in the scheme and said that it was her glamorous appearance that made people think her a “villain.” She was among the officials affected by the temporary suspension Mr. Putin announced.
With Russia’s representation in Rio at stake in both Olympic and Paralympic competition, the country is lobbying for its flag to fly at the Games.
Mikhail Gorbachev, the last president of the Soviet Union, has appealed to Mr. Bach on Russia’s behalf, calling a collective ban unacceptable in a letter sent on Friday.
Russia was notified of the proceedings against its Paralympic team on Friday, a Paralympic spokesman said, and the country would have an opportunity to weigh in ahead of officials’ formal vote to suspend on Aug. 1; the Paralympic Games open on Sept. 7 in Rio. With 263 athletes, Russia would have the third-largest delegation at the Paralympics.
Though early allegations of widespread doping in Russia had centered on Olympic track and field, recent investigations have concluded that the schemes transcended any one individual sport, touching disciplines as disparate as bobsled and weight lifting.