Russia's anti-doping agency chief Yuri Ganus believes data handed from the Moscow laboratory to the World Anti-Doping Agency has been intentionally manipulated, he told German magazine Der Spiegel on Wednesday, and expects "tough punishment".
"The changes to the data are so big and significant that it can't be an accident," said Ganus, RUSADA's director general.
"They aren't stacks of data that have been deleted but they have been modified or back-dated in someways. Someone has tried massively to hide the information. It could also be a questions of athletes names," he added.
Sports minister Pavel Kolobkov said earlier in the day Russia has responded in full to all questions raised by WADA concerning "inconsistencies" in data from Moscow's anti-doping lab.
Russia's Athletics Federation has been banned from international competition since 2015 over a vast state-run doping conspiracy, and the International Association of Athletics Federations last month extended the ban.
Also in September, WADA gave Russia three weeks to address the questions pertaining to data handed over by the Moscow lab from the years 2011-2015 when state-sponsored doping was prevalent.
Ganus, who was appointed in 2017, added the changes could have also been carried out in more recent years.
"We're talking months, the last modifications date back to December 2018 and January 2019," he said.
"The punishment is going to be very tough, because it won't be the first time that Russia has broken the laws. Participation at the Olympics in Tokyo 2020 and Beijing 2022 (Winter Olympics) are at stake," he added.