Russian football was the target of fresh doping allegations on Wednesday with claims of widespread urine sample tampering levelled by Richard McLaren, author of an explosive report into Russian doping.

The Canadian lawyer told German TV channel ARD he had fresh evidence indicating that positive tests taken from Russian players were swopped with clean samples.

McLaren said the World Anti-Doping Agency had seized 155 samples from 2018 World Cup hosts Russia for re-testing, with FIFA kept informed.

According to WADA's special anti-doping investigator an exchange of emails between high-ranking Russian officials dating back to 2015 detailed the urine sample swop scam.

He told ARD: "We have some information where there's reference to trying to find a sample which would be suitable possibly for swapping that gives rise to a suspicion that there is a bank of clean samples somewhere, not in the lab, maintained by somebody, and that it's being used, with respect to footballers.

"We would conclude from what information we do have that there must be a different system operating in football than the ones that we reported on (in other sports)."

McLaren fears this is "the tip of the iceberg".

"We'd like to know what's underneath the waterline," he told ARD.

He says the batch of samples taken by WADA and awaiting analysis will reveal one of two things: "Either there's been tampering with the caps or the contents could have been changed.

"Or the contents haven't been changed but there may be prohibited substances in there."

Neither FIFA nor the Russian authorities accepted ARD's invitation to respond to the allegations which follow last weekend's report in a British newspaper that Russia's entire 2014 World Cup squad was under FIFA investigation for doping.

The Mail on Sunday wrote that the Russian players are being probed by FIFA as part of a broader scandal over allegations of state-backed doping in the country.

Russian deputy Prime Minister Vitaly Mutko blasted the report as "nonsense" and insisted that there has never been any problem with doping in the Russian game.

And FIFA insisted all players including all of the Russian squad underwent pre-competition and post-match tests in Brazil.

"All of which resulted negative," a spokesman for football's governing body said on Sunday.

McLaren's bombshell report in 2015 uncovered state-sponsored doping in Russia, with the country's track and field team banned from the 2016 Rio Olympics.

A second report released by McLaren in December highlighted 31 tampered doping samples from footballers.