Eighteen weightlifters from six countries are suspected of supplying false urine samples after a World Anti-Doping Agency (WADA) investigation found evidence of "doppelgangers" being used to impersonate athletes, WADA said Thursday.

WADA said the 18 cases, uncovered as part of a wide-ranging investigation into the scandal-tainted International Weightlifting Federation (IWF), will be forwarded to the International Testing Agency for review.

A WADA statement said the fraudulent urine samples had been uncovered after the agency's investigators developed a new methodology to identify substituted urine with help in part from confidential sources and analysis experts.

DNA analysis found 18 cases and evidence that lookalikes had been used to impersonate athletes during the sample collection process, to ensure that "clean" urine was provided.

The countries of the athletes involved were not disclosed.

"WADA is appalled by what its Intelligence and Investigations Department has uncovered in this investigation," WADA President Witold Banka said in a statement. "For too long, clean weightlifters have had to deal with an entrenched culture of doping in their sport, where the promotion of fear ensured that the truth remained hidden and that those who wanted to do the right thing were isolated.

"Once again this has shown the importance of whistleblower information and the positive difference that can be made when people with information have the courage to come forward. Intelligence from well-placed confidential sources, coupled with the diligent work of WADA Intelligence and Investigations, is delivering significant results across a host of investigations.

Banka said the results of WADA's probe had highlighted the need to potentially strengthen the agency's investigatory powers, including granting "unfettered access to all relevant internal documents and servers within the organization under investigation."

The investigation into urine substitution is one of several areas WADA investigators are digging into.

The probe is also studying claims that a high-ranking member of the IWF was paid to promote Russian interests and to protect Russian athletes from being caught by drug-testers, as well as a drug cover-up in Romanian weightlifting.

Weightlifting has been in turmoil since January when a documentary by German TV channel ARD revealed what it described as a "culture of corruption" in the sport intended to mask the use of doping. 

Hungarian Tamas Ajan, 81, chairman of the IWF for 20 years after serving as its secretary general, rejected the accusations as "lies" before being pressured into resigning in April.

According to the documentary, until 2017 high-level weightlifters were being exempted from many doping controls, and test results were being altered in exchange for bribes.