The International Olympic Committee on Sunday decided not to hit Russia with a blanket ban for the Rio Games over state-run doping, but said each sports federation needed to establish a competitor's individual eligibility.
Federations "should carry out an individual analysis of each athlete's anti-doping record, taking into account only reliable adequate international tests, and the specificities of the athlete's sport and its rules, in order to ensure a level playing field," the IOC said in a statement.
It comes after the IOC held showdown talks on whether to ban Russia from the Rio Games over rampant doping that sparked the Olympic movement's worst crisis in decades.
The Russian athletics team was already banned from Rio for state-sponsored doping.
An independent report last week for the World Anti-Doping Agency (WADA) said Russia's sports ministry directed a vast doping program with support from the state intelligence agency that saw thousands of tainted urine samples destroyed or swapped for clean ones.
The cheating affected 30 sports and went on during the 2014 Sochi Winter Games and other major Olympic and international events, according to the WADA report last week by Canadian law professor Richard McLaren.
Tough criteria for Russian athletes
IOC president Thomas Bach stressed Sunday that Russian competitors have to pass an extremely rigorous set of criteria before being cleared for the Rio Games.
"We have set the bar to the limit," Bach told reporters after the IOC decided against a blanket ban on the entire Russian team over state-run doping.
Each Russian Olympic hopeful must be individually cleared by their respective sports federation. An expert from the Court of Arbitration for Sport must then approve the federation's decision, with the IOC having the final word.
That process must be carried out for the more than 300 athletes nominated for Rio by the Russian Olympic Committee (ROC) within two weeks, with the Games set to start on August 5.
"This is a very ambitious timeline, but we had no choice," Bach said.
The stunning allegations about Russian cheating released this week by the World Anti-Doping Agency forced the IOC to take aggressive action without the luxury of time, Bach explained.
Russian athletes "have to assume a collective responsibility, "for operating in such a corrupt system, he said.
But rather than implementing an outright ban on the whole country, the IOC wanted to send "a message of encouragement to the clean Russian athletes to show that they are clean."
"It's fine to talk about collective responsibility," Bach said, "but at the end of the day you have to be able to look in the eyes of every athlete concerned."
Asked how he would respond to critics accusing the IOC of treating Russia too softly, Bach said: "read the decision," stressing that the ROC was being treated more harshly than every other national Olympic committee.
Russia hails decision
Russia hailed the IOC's decision.
"It was objective and taken in the interests of world sport and the unity of the Olympic family. We are grateful to the IOC for such a decision," sports minister Vitaly Mutko told R-Sport news agency.
He added later in televised comments that he was convinced that the "majority" of the Russian team would meet strict criteria to compete.
"As far as the criteria announced for the Russian team on the eve of the Olympic Games they are of course very tough," Mutko said.
"It is a specific challenge for our sportsmen but I am absolutely sure that the majority of the Russian team will meet the criteria."
Russian sports bosses welcomed the decision and began looking forward to the the competition in Rio.
"I don't see any problem with the participation of our tennis players at the Olympics," Shamil Tarpishev, the president of Russia's tennis federation told TASS news agency.
"I am sure that the whole team that we've named will compete at Rio."
The head of Russia's swimming federation Vladimir Salnikov told R-Sport that he was waiting to hear from the international swimming federation if the new IOC criteria would rule out swimming star Yulia Efimova, who tested positive for banned substance meldonium.
Separately, an IOC ethics commission also ruled that 800m runner Yuliya Stepanova, who turned whistleblower on doping in Russian athletics, could not go to Rio even as a neutral.
Russia's track and field team is already barred from Rio and the decision to exclude Stepanova, who served a doping ban exposing the rot inside Russian athletics, was greeted with approval by officials.
"It is correct that they did not let in Stepanova. I support that decision," athletics federation head Dmitry Shlyaktin told R-Sport.
US anti-dopers react
US anti-doping chiefs blasted the IOC for creating "a confusing mess" over the Russian doping scandal, claiming they lacked "decisive leadership" by opting against a blanket Rio ban for Russia.
"Disappointingly, in response to the most important moment for clean athletes and the integrity of the Olympic Games, the IOC has refused to take decisive leadership," said Travis T. Tygart, the chief executive of USADA, the American anti-doping body.
"The decision regarding Russian participation and the confusing mess left in its wake is a significant blow to the rights of clean athletes.
"It is so frustrating that in this incredibly important moment, they would pass the baton to sports federations who may lack the adequate expertise or collective will to appropriately address the situation within the short window prior to the Games. The conflict of interest is glaring."
USADA also hit out at the decision to ban doping whistleblower Yuliya Stepanova from taking part in the Olympics.
"The decision to refuse her entry in to the Games is incomprehensible and contrary to CAS precedent. The attempt to enforce it will undoubtedly deter whistleblowers in the future from coming forward," said Tygart.
The games begin August 5.