The head of Ukraine’s anti-doping agency resigned on Wednesday, the sports ministry said, after the World Anti-Doping Agency (WADA) accused his organisation of violations going back years.

WADA said the National Anti-Doping Organisation of Ukraine (NADC) had given athletes advance notice of what were supposed to be random out-of-competition tests in a scheme dating back nearly a decade.

Ukrainian sports minister Vadym Guttsait said in a statement that the NADC had violated international testing standards and that “therefore, today, the director of NADC Ivan Kurlischuk and his deputy Yaroslav Kruchek resigned.”

“The ministry states that we take a clear stance in the fight against doping and will not allow anyone to violate anti-doping rules,” the statement read.

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The WADA investigation – dubbed “Operation Hercules” – uncovered evidence that since 2012 the NADC had routinely tipped off athletes prior to testing. Instead of conducting random, out-of-competition tests – a key pillar of the fight against drug cheats – the NADC would contact athletes to arrange for testing at the organisation’s offices the following day.

Investigators also found that the NADC categorised at least six in-competition athletes samples as out-of-competition samples ahead of the postponed Tokyo Olympics. The six samples in question were re-analysed by WADA but came back negative.

The Operation Hercules findings will now be turned over to WADA’s Compliance Review Committee for possible sanction.