The World Anti-Doping Agency (WADA) announced Monday a probe into "inconsistencies" in laboratory data provided by Russia, raising the possibility of a fresh ban on the country in the build-up to the Tokyo Olympics.
WADA said it had given Russia three weeks to respond after problems with the data came to light.
The revelation opens the door for fresh sanctions against Russia, which was banned from the Pyeongchang 2018 Winter Olympics over doping.
"Ensuring the authenticity of the Moscow (laboratory data) was one of the critical conditions imposed by the ExCo for RUSADA to maintain its compliance," said a statement after WADA's Executive Committee meeting in Tokyo.
WADA has previously warned that it would take the "most stringent sanctions" if any of the data was found to have been tampered with.
Russia handed over thousands of files and samples from its Moscow anti-doping laboratory in January, fulfilling a key condition for its reinstatement by WADA last September.
The Russian Anti-Doping Agency (RUSADA) had been suspended for nearly three years over revelations including a systematic conspiracy to switch tainted samples at the 2014 Sochi Winter Olympics.
During its suspension by WADA, the International Olympic Committee allowed Russia to take part in the 2016 Rio Olympics, but Russian athletes at the 2018 Pyeongchang Winter Games had to compete under a neutral flag.
However, athletics body the IAAF has maintained a ban on Russia since November 2015, although many of its athletes are given special dispensation to compete under a neutral banner.
The IAAF is due to re-examine the case for reintegrating Russian athletes ahead of the World Athletics Championships, which start in Doha on September 27.
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