The World Anti-Doping Agency (WADA) has issued further allegations to existing charges of systematic doping and cover-ups of positive doping tests in Russia
The news comes ahead of Friday's Vienna meeting of the council of the ruling athletics body IAAF, which is to decide whether to prolong the suspension of the Russian athletics federation, which could keep Russia out of the August 5-21 Games.
The new WADA report published late Wednesday alleges that 736 planned doping tests of Russia competitors were thwarted through various means between February 19 and May 29.
Doping inspectors in Russia were obstructed during that time period, with reports of intimidation by agents from Russia's FSB security service. In some cases, packages containing samples for testing were tampered with.
Test subjects gave false information about their whereabouts and tried to dodge inspectors at competitions. In some cases, military facilities were given as athlete locations, but they required special authorization to access.
In one case, a test subject apparently tried to cheat a urine sample using fluid from a bag concealed inside her body, only to try to bribe the inspector when discovered.
The allegations are the latest blow for Russia which had its athletics federation suspended in November after a first WADA report spoke of systematic doping in the country and cover-up attempts. The Moscow anti-doping lab was also stripped of its accreditation.
Prominent Russian athletes, including former swimming great Alexander Popov, have meanwhile appealed to the International Olympic Committee (IOC) to let clean Russian athletes compete in Rio, saying the existing doping cases "should not jeopardize the career of innocent athletes."
This appears to be seen as a compromise solution while others like the German athletics federation (DLV), in another open letter to the IOC, want Russia suspended because athletes cheated, the IOC and Olympic ideals "have been deceived" and an equal opportunity competition could not guaranteed.
The IOC however says that it has no influence on the issue and that the final decision is with the IAAF and its new president Sebastian Coe.
Battered by the doping allegations and those of corruption during the old IAAF leadership of Lamine Diack - who is under criminal investigation in France - the ruling is seen as a serious test for the IAAF to restore credibility.
The basis of discussion in Vienna is a report from an IAAF task force led by Norway's Rune Andersen, which has monitored Russia's attempts to comply with conditions set by the IAAF.
Coe was quoted as saying he has full faith in Andersen and his team, and would not shy away from what would be the first ever ban of a whole team if Russia is not compliant.
Russian sports minister Vitali Mutko and others have pledged full cooperation since November, and Russia has the right to appeal an extended ban before the Court of Arbitration for Sports.