Russian officials handed over data which contained “inconsistencies” to World Anti-Doping Agency chiefs, the body set up to combat drug cheating in sport has said.
Wada has now opened compliance proceedings against the Russian Anti-Doping Agency (Rusada).
It suspects data may have been manipulated before being passed on.
Russia was asked to hand over data from its Moscow laboratory to show it complied with global anti-doping rules.
It was a key step taken towards Russia’s reintegration back into the sporting fold following its suspension over a state-sponsored doping programme.
Wada said on Monday its executive committee “was informed that further investigation of inconsistencies in Moscow laboratory data had led Wada to open a formal compliance procedure against Rusada”.
The body says it is “pursuing the matter robustly” and Russia has been given three weeks to explain the inconsistencies.
In comments reported by the Russian news agency Tass, the country’s sports minister Pavel Kolobkov said: “What exactly are these discrepancies and what are they related to?
“Experts in digital technology from both sides are already in collaboration. For our part, we continue to provide all possible assistance.”
Russia had missed deadlines to hand over the data before finally granting Wada access to the Moscow anti-doping laboratory in January.
BBC sports editor Dan Roan said the discovery of “inconsistencies” in the data and the suggestion it had been tampered with could lead to renewed pressure on the International Olympic Committee to ban Russia from next year’s Tokyo Games.
It will also ensure a suspension of Russia by athletics’ governing body, the IAAF, continues, he added. The World Athletics Championships start in Doha on Friday.
BBC Sport understands that senior Wada officials were briefed last month that the organisation’s experts had found evidence some data may have been manipulated before being passed over to an inspection team.
A landmark Wada-commissioned report in 2016 found Russia operated a state-sponsored doping programme for four years across the vast majority of Olympic sports.
Russia was told it had to meet two criteria before Rusada could be reinstated after a three-year suspension: accept the findings of the McLaren report into state-sponsored doping, and grant access to Moscow’s anti-doping laboratory.
However, Wada’s stance softened, and after offering a compromise over the ‘roadmap’, its compliance review committee (CRC) controversially recommended reinstatement in September 2018 before the second condition had been met, prompting fury from many athletes and anti-doping organisations.
In December, Russia missed a deadline to grant access to its lab, but the following month an inspection team was finally allowed to retrieve the data.
Although it was accused by many of being too soft on Russia, Wada’s leadership hailed the breakthrough, insisting it would enable it to identify potential cheats, and allow international federations to pursue cases against them.
CRC chairman Jonathan Taylor – a British lawyer – also warned that if the data was found not to be authentic, he would “propose serious consequences”.