By Karolos Grohmann
LAUSANNE, Switzerland (Reuters) - Positive re-tests of doping samples from the 2008 and 2012 Olympics have left IOC President Thomas Bach with real concerns about Russia, as well as the sport of weightlifting, he said on Thursday.
About 100 Russian athletes were banned from competing at the Rio de Janeiro Games in August following revelations of a widespread and state-backed doping system in the country.
Another World Anti-Doping Agency (WADA) commissioned report will be published on Friday and is expected to pile more pressure on the country whose federation remains banned from athletics.
Re-tests of doping samples from the Beijing and London Games conducted by the International Olympic Committee (IOC) have caught 101 doping offenders, with Russia having the most cases.
Of the 74 named athletes, 27 are Russians, with 16 positive tests coming from 2008 and 11 from 2012.
"The first analysis shows already that re-testing raises concerns with regard to some countries, in particular Russia, and with regard to some sports, in particular weightlifting," said Bach, who earlier this year refused to authorize a blanket ban of Russia from the Rio Games.
"We will have to analyze this in more depth and consult with the WADA about this situation."
The sports with the most cases in those Games were weightlifting, with 38 positive re-tests, and athletics with 31. The other three sports affected by the re-tests - cycling, swimming and wrestling - had single digit positives.
A total of 27 athletes have been stripped of their medals, including one gold, from the Beijing Games while 16 lost their medals following the London re-tests, five of them gold.
The IOC re-tests samples from past Olympics as it looks to stop cheats from competing in the next Games.
The report on Friday by Canadian lawyer Richard McLaren is the second part of his investigation into Russian doping in sport. The first part in July led to a partial ban of Russian athletes for Rio.
Bach refused to speculate on the content but said if athletes had manipulated the doping system then he would favor a lifetime ban from the Games.
Previous IOC efforts to keep doping offenders who had served a suspension from going to the Games had been rejected by the Court of Arbitration for Sport.
"If there is an athlete or official who would have been part of such a system (of manipulation) I would not like to see this persona again at the Games in whatever function," Bach said.
"This for me would present such aggravated circumstances, the logic would be life ban and exclusion from Olympic Games for life."
(Reporting by Karolos Grohmann, editing by Mitch Phillips)