BEIJING - There is no doubt that the recent Fancy Bears attacks are Russian retaliations against the agency and the global anti-doping system, WADA Director General Olivier Niggli said Wednesday.

The World Anti-Doping Agency (WADA) condemned Russia for illegally gaining access to its Anti-Doping Administration and Management System (ADAMS) and exposed personal medical data of 29 athletes.

Kremlin immediately responded to WADA's accusations, denying any Russian involvement in the hacking.

"We are also very concerned because they have the same data on the Russian athletes and we can also be victims," Russian Sport Minister Vitaly Mutko said Wednesday, referring to the Russian boxer Mikhail Misha Aloyan who also appeared in the leaked lists.

A hack team named Fancy Bears exposed through its Twitter account a WADA document on Tuesday, which revealed a list of American athletes using banned substances, including American gymnast Simone Biles, and tennis players Serena and Venus Williams

It then revealed another batch of WADA document on Thursday containing the personal medical data of athletes from eight countries, including American women's basketball player Elena Delle Donne.

WADA confirmed the authenticity of the leaked data which recorded 29 athletes being granted Therapeutic Use Exemptions (TUEs). TUEs could be a waiver for athletes to use an otherwise-prohibited substance for medical needs.

According to the leaked data, Serena and Venus Williams were granted several waivers to take banned substances from 2010 to 2015. Biles tested positive for methylphenidate in August, but not disqualified, winning four golden medals in the 2016 Rio Olympics.

Serena, who won a silver medal in mixed doubles in the 2016 Rio Olympics, said via her agent that her exemptions were "reviewed by an anonymous, independent group of doctors, and approved for legitimate medical reasons."

"I have followed the rules established under the Tennis Anti-Doping Program in applying for, and being granted, 'therapeutic use exemption,'" she said.

In a statement, USA Gymnastics also said Biles was approved for an exemption and had not broken any rules.

"Please know, I believe in clean sport, have always followed the rules, and will continue to do so as fair play is critical to sport and is very important to me," Biles posted on her Twitter account.

The International Olympic Committee (IOC) said Tuesday that it "strongly condemns such methods which clearly aim at tarnishing the reputation of clean athletes," and therefore granted American athletes' use of banned substances as legitimate.

"Anybody who is an athlete and is subject to an antidoping program, like the Williams sisters, is subject also to getting ill and having medical conditions," said Stuart Miller, director of the International Tennis Federation's anti-doping program.

"The program is a rigorous and necessary part of elite sport; and, it has overwhelming acceptance from athletes, physicians and all anti-doping stakeholders," according to a statement published Friday on WADA's official website.

The annually updated list of banned substances is finalized by a panel of three medical experts selected by WADA, which has the power to veto primary decisions made by sports organizations.

The final decisions are made with consideration of whether an athlete's performance will unfairly benefit, WADA official Niggli said.

On the other hand, Alan D. Rogol, a professor at the University of Virginia who works with the United States Anti-Doping Agency (WSADA), called some of WADA's decisions "no-brainers" which involved little mental efforts.

Unlike the American athletes who were given waivers to use prohibited substances, Russia's track and field team and many other athletes were banned from participating in the 2016 Rio Olympics after a WADA report said there was state-sponsored doping in the country.

Although the name Fancy Bears is reportedly connected with a Russian cyber-espionage group called Tsar Team (APT28), there is still no solid evidence to prove that the attacks were originated from Russia.

Despite WADA's allegations, the identity of the hackers is still undetermined. The hackers' website, for example, appears to be registered in Paris, and has Korean characters in the code and a server based in California.

In a statement posted to its website early Tuesday, the hack team proclaimed its allegiance to Anonymous, a loosely associated international network of activist and hacktivist entities including those from the United States.

Nevertheless, US media seemed to declare Russia guilty. Besides condemning the hacking attacks as "criminal acts" and "cyberbullying of innocent athletes", some referred to the hack team directly as "Russian hackers."