Another 45 athletes, including 23 medallists, have tested positive for forbidden substances in a second round of retests of samples from the 2008 and 2012 Olympics, the International Olympic Committee (IOC) said on Friday.
The IOC said that 30 retests from Beijing 2008 returned positive, with the athletes coming from four sports and eight countries.
While the Beijing results are provisional findings, pending the analysis of the b-sample, the 15 tests from London 2012 are positives and from two sports and nine countries.
The 23 medallists are all from the Beijing retests, the IOC said.
In total, 98 athletes have tested positive in two rounds of retests from the two Games in which 1,243 samples were examined. The 840 Beijing retests saw 60 adverse findings and the 403 London tests 38.
"All athletes found to have infringed the anti-doping rules will be banned from competing at the Olympic Games Rio 2016," the IOC said, looking ahead at the August 5-21 Games in Brazil.
IOC president Thomas Bach said: "The new reanalysis once again shows the commitment of the IOC in the fight against doping."
The IOC said it will conduct two further waves of retests from the 2008 and 2012 Games, with the analysis continuing until after Rio.
Using the latest scientific analysis methods, the IOC said its second wave of retests of the Beijing samples focussed mainly on medallists and that the 2008/2012 retests "followed an intelligence-gathering process that started in August 2015 and included the World Anti-Doping Agency (WADA) and International Federations (IFs)."
The IOC did not identify the athletes and countries for confidentiality reasons but said all parties have been informed.
The news came as the IOC must decide whether or not to ban all Russian athletes from competing in Brazil, after allegations of state-organised doping in Russia in various sports, made in a report by a WADA commission.
Russia's athletics team is already banned, the measure from the ruling athletics body IAAF confirmed Thursday by the Court of Arbitration for Sport.
The IOC said it will make a decision by Tuesday at the latest, with an executive board meeting set for Sunday.
Of the 53 athletes caught in the first wave of IOC retests from 2008 and 2012, 22 athletes were from Russia, according to the nation's Olympic Committee.
Kremlin spokesman Dmitry Peskov meanwhile on Friday ruled out a crisis meeting between Russian President Vladimir Putin and Bach, while expressing hope the IOC will allow its clean athletes to compete in Rio.
"Everyone in Moscow is preparing for the Olympic Games, and Moscow thinks that all athletes who have not been tarnished by any suspicions, all athletes that were not accused of doping should have the right to perform at the Olympic Games. That’s what we hope IOC’s decision will be," the Tass news agency quoted Peskov as saying.