The International Olympic Committee has said athletes from Russia and Kenya will only be able to compete at the Rio Olympics if they pass an "individual evaluation" to prove they have not been doping.
The unprecedented move was agreed at an emergency IOC summit in Switzerland following last week's decision by the International Association of Athletics Federations to maintain its doping ban on Russian athletes.
With the World Anti-Doping Agency declaring both Kenya and Russia "non-compliant" with its rules, IOC president Thomas Bach said athletes from those countries could no longer be "presumed innocent".
Any competitor from Russia or Kenya, which has also been mired in doping controversy, will need to be declared eligible by their sport's international federation in order to compete in the games.
However, Russian track and field athletes remain banned from Rio after the IOC offered "respect, approval and support" for the blanket ban on them, extended on Friday by world athletics' governing body for systemic doping.
Before the IOC announcement, Russian Olympic chief Aleksander Zhuko indicated clean Russian track and field athletes will appeal their Olympic ban at the Court of Arbitration for Sport.
If the IAAFs allows "special clearance" for any Russian track and field athlete to compete, it will be under the Russian flag rather than an Olympic of neutral one.
Bach has also called on WADA to hold a global anti-doping conference in 2017 to fully review the system.
