The Russian and Olympic flags during the closing ceremony of the 2014 Winter Games in Sochi, Russia. (Kay Nietfeld/EPA)

Dozens of former Olympic athletes could be barred from the upcoming Summer Games in Rio de Janeiro, the International Olympic Committee announced Tuesday, after drug testers completed an initial wave of analysis of old samples in the aftermath of a series of reports alleging systemic, state-supported cheating by Russia.

Testing of 454 urine samples from the 2008 Summer Olympics in Beijing revealed suspicious samples from 31 athletes from 12 countries, the IOC said. The testing was focused on athletes who could participate in this summer’s Games, and the IOC said it will soon test 250 samples from the 2012 Summer Games in London. The athletes implicated Tuesday were not identified by the IOC, which said it had started notifying the countries involved.

While athletes from 12 countries were implicated Tuesday, the unprecedented mass analysis of old samples was triggered solely because of allegations involving one country — Russia. An investigation by the World Anti-Doping Agency last year found a “deep-rooted culture of cheating” in Russian athletics, prompting an ongoing global ban of the nation’s track and field athletes that may keep them out of the Rio Games.

Documentaries and published reports over the past two years — including stories in the past two weeks by CBS’s “60 Minutes” and the New York Times — have alleged state-sponsored cheating and covert operations to compromise drug testing in Russia, culminating with a sophisticated scheme to subvert anti-doping efforts at the 2014 Winter Olympics in Sochi.

A 2008 photo shows a protective fence with the Beijing 2008 logo outside the National Stadium in the Chinese capital. (Petr David Josek/AP)

The U.S. Attorney’s Office in the Eastern District of New York has opened a criminal investigation into possible state-sponsored doping by top Russian athletes, the Times reported Tuesday. Spokesmen for the U.S. Attorney’s Office, the Justice Department and the FBI declined to comment.

IOC President Thomas Bach, in a news release, termed Tuesday’s IOC announcement “a powerful strike against the cheats we do not allow to win” and said the action was spurred by the “worrying allegations against the laboratory in Sochi.”

The IOC keeps urine samples of Olympic athletes for 10 years, and it’s not surprising that re examining old samples would uncover new positive tests for banned drugs because testing methods constantly evolve. The World Anti-Doping Agency — which oversees drug testing for the Olympics — confirmed in its own statement Tuesday that this wave of retesting has been prompted by allegations against Russia.

This month, two reports quoting self-described whistleblowers from Russia have outlined allegations that support last year’s WADA investigation. First, a former elite Russian runner told “60 Minutes” she took a powerful regimen of anabolic steroids and banned endurance-boosting substances under the direction of her coaches and medical staff. Then the former director of Russia’s anti-doping lab went public in the New York Times with a description of drug testing sabotage from the Sochi Games that, if true, ranks among the more sophisticated drug cheating schemes in sports history.

Grigory Rodchenkov claimed he worked for years to help his country’s top athletes take banned drugs and escape detection. He synthesized a literal steroid cocktail — it included alcohol to help speed absorption into the blood — for Russian athletes, and then when the 2014 Winter Games came to Sochi, he worked with a small team to replace tainted urine samples with clean ones.

Each night during the Sochi Olympics, Rodchenkov said, he and others surreptitiously removed Russian urine samples via a small hole secretly cut in a wall at the Olympic anti-doping lab. The glass bottles used for drug testing, which are developed by a Swiss company called Berlinger, are supposed to be tamper-proof, but Rodchenkov claimed Russian intelligence developed a way to open them.

“I’ve seen skullduggery over the years related to Olympic samples . . . but the case of Sochi is really pretty far out there. . . . We thought the system was pretty bulletproof,” Don Catlin, a UCLA anti-doping scientist and one of the founders of modern sports drug testing, said in a phone interview Tuesday.

“I would love to just dismiss it, but the details are so exact and precise that you have to think that maybe it’s true,” Catlin said.

Catlin has worked with Rodchenkov, he said, and the American anti-doping expert expressed dismay at the apparent revelation that a man he thought was on the side of those working to root out drug cheating in sports was actually helping athletes take banned substances and get away with it.

“It’s just more evidence of how difficult it is to do anti-doping work. People have suspected it for years, but now we’re getting more information that confirms that,” Catlin said.

Rodchenkov fled Russia last year fearing for his life, he said, after he was forced to resign in the aftermath of the WADA report. He is in Los Angeles and working with a filmmaker, Bryan Fogel, on a documentary about drug cheating in sports.

WADA has said it will investigate Rodchenkov’s claims, and he has said he will aid their investigation. His allegations have renewed calls from some doping experts to expel Russia from Olympic sports.

“Throw them out,” said John Hoberman, a University of Texas historian and doping expert. “There’s no evidence whatsoever that the Russians have any intention of changing. . . . What they are going to try to change, of course, is the world’s perception of what is going on there. They will do this Kabuki dance to simulate a reform process.”

Hoberman expressed skepticism that the IOC and WADA are willing to impose such a drastic penalty on one of the world powers.

“They cannot pull the trigger and say enough is enough,” Hoberman said. “You can’t negotiate with a conscienceless political leadership that is fixated on winning medals for its own political reasons.”

For months, Russian sports officials have been mostly defiant, claiming reports by WADA and documentaries from a German television station alleging systemic cheating were baseless, politically motivated attacks. Russian officials recently have spoken with newfound contrition, though.

In a piece written for Britain’s Sunday Times, Russian sports minister Vitaly Mutko apologized for “serious mistakes” made by his country’s coaches and athletes, and pleaded for the global ban on Russian track athletes to be lifted in time for this summer’s Olympics.

“We believe passionately in the Olympic spirit and values,” Mutko wrote.

Matt Zapotosky and Julie Tate contributed to this report.