The International Olympic Committee received an urgent letter from more than a dozen national anti-doping organisations on Wednesday night urging it to immediately suspend the Russian Olympic Committee and provisionally ban all Russian athletes from the Rio Olympics.

The letter, seen by the Guardian and addressed directly to the IOC president, Thomas Bach, warned him that he needed to fulfil his obligation to take the toughest possible sanctions against “institutionalised, government-run doping and abuse of athletes” to ensure the integrity of the Olympic Games.

Dick Pound fears IOC reluctant to ban entire Russia team from Olympics Read more

However, it said Russian athletes could compete in Rio under a neutral flag if a task force approved by the IOC and World Anti-Doping Agency verified they were clean, “thereby striking a fair balance between your stated concerns between collective responsibility and individual justice so that no truly clean elite Russian athlete is barred from the Rio Olympic Games”.

The letter, which was signed by 14 heads of anti-doping organisations including from the United States, Germany, Japan and Spain, comes amid growing fears that the IOC is cooking up a deal to allow the majority of the 386-strong Russian team to compete in Rio. Those were made public on Wednesday when the longstanding IOC member Dick Pound broke ranks to warn that the organisation was “very reluctant” to issue a blanket ban.

However, Joseph de Pencier, CEO of iNADO, which represents national anti-doping organisations, warned the IOC that they should expect more revelations from professor Richard McLaren, whose report on Monday detailed widespread state-sponsored doping in Russia.

De Pencier said: “In the face of the McLaren Report, and the additional findings likely to come from professor McLaren’s team in coming days, the IOC has an unmatched opportunity to do the right thing in the interests of clean sport and clean athletes around the world.

The IOC will have our support in acting decisively and unequivocally showing that clean sport is at the heart of Olympic values.”

The letter also warned the IOC that a plan to allow international federations from each sport to separately decide whether to allow Russian athletes to compete – which is favoured by some members of the IOC’s executive board – was not feasible. “There is simply insufficient time remaining before the Rio Games and insufficient time and expertise available to the IFs within the 16 days remaining before the Games to accomplish the individualised analysis recommended by the IOC,” it says.

“Moreover, there is the risk that individualised individual federations’ processes implemented at this late date would be subject to disparities and inconsistencies which would further undermine the Wada Code goal of having a uniform, harmonised world anti-doping programme.

Meanwhile, later on Thursday the court of arbitration for sport in Lausanne will issue its verdict on whether to uphold the ban on 68 Russian track and field athletes from competing in Rio. On one side stands the IAAF, the governing body of athletics, which argues that the staggering evidence of state-sponsored doping in Russia that has built up in the past year means that no athlete inside the system can be trusted to be clean. On the other is the Russian Olympic Committee, which insists that those athletes who have never failed a test should be allowed to compete.

The IOC will be watching the verdict closely. It has decided against a quick decision over whether to exclude Russia from Rio while it waits for legal advice over whether such a ban would be enforceable, as well as Cas’s decision.

If Cas does uphold the ban, most observers expect it will increase the pressure on the IOC to consider a broader ban on all Russians at the Olympics. But Pound, who was also a former president of the World Anti-Doping Agency, believes the IOC will not budge.

“I do get the impression, reading between the lines, that the IOC is for some reason very reluctant to think about a total exclusion of the Russian team,” he said. “But we’ve got institutionalised, government-organised cheating on a wide scale across a whole range of sports in a country. If you do take the tough line and walk the walk as well as talking the talk, I think a significant portion of the world would be very pleased.”

The Russian Olympic Committee president, Alexander Zhukov, said he expected the issue to be resolved by the end of the week, although the IOC has since suggested any decision could take up to seven days.