In another blow, the International Association of Athletics Federations (IAAF) maintains a ban on the Russian athletics federation pending analysis of the data.
The World Anti-Doping Agency (WADA) on Monday gave Russia three weeks to explain "inconsistencies" in a cache of laboratory data handed over to investigators, raising the possibility of a fresh ban on the country in the build-up to the Tokyo Olympics.
Russia stands to be declared non-compliant by WADA if it fails to explain why evidence of some positive tests handed over by a whistleblower doesn't show up in data provided by Moscow's anti-doping laboratory in January.
If Russia challenges an eventual suspension by WADA the case will go to the Swiss-based Court of Arbitration for Sport, whose decision will be binding on sports bodies, including the International Olympic Committee.
"Forensic experts have looked at what we got from whistleblowers, what we got from Russia and they noticed some inconsistencies," WADA director general Olivier Niggli said after an executive committee meeting in Tokyo.
"Then they studied the differences and this came to a situation where there are some questions that need to be asked and answered."
WADA has previously warned that it would take the "most stringent sanctions" if any of the data was found to have been tampered with.
Russian Sports Minister Pavel Kolobkov said WADA and RUSADA, the Russian anti-doping agency, would look into "inconsistencies."
"Digital experts from both sides, who are already in touch, will see what the discrepances are about and what they are connected to. As far as we are concerned, we continue to help in any way possible," he said in comments released by his ministry.
Russia handed over thousands of files from its Moscow anti-doping laboratory in January, fulfilling a key condition for its reinstatement by WADA last September.
RUSADA had been suspended for nearly three years over revelations of wrongdoing including a systematic conspiracy to switch tainted samples at the 2014 Sochi Winter Olympics.
During its suspension by WADA, Russia was allowed by the International Olympic Committee to take part in the 2016 Rio Olympics, but Russian competitors at the 2018 Pyeongchang Winter Games had to take part under a neutral flag.
IAAF maintains Russia ban
The IAAF said Monday it would maintain a ban on the Russian athletics federation pending analysis of data from the Russian anti-doping laboratory covering the 2011-2015 period when state-sponsored doping was prevalent.
"The council endorsed the strongest recommendation we've probably had from the taskforce that Russia remains suspended," International Association of Athletics Federations president Sebastian Coe said following a meeting of the body's council in Doha ahead of the World Championships.
Though the Russian federation remains banned, athletes from Russia have been competing for years as neutrals with 118 due to participate in the World Athletics Championships which get underway in Doha Friday.