"Sadly Nikita has passed away. What happened looks like a massive heart attack," Khabriyev said, adding that he was not aware of Kamayev having had heart problems before.
Kamayev resigned along with three other RUSADA top officials after a report by a World Anti-Doping Agency (WADA) independent commission accused Russia of routine violations of testing standards and allowing suspended athletes to compete.
Both RUSADA and Moscow`s anti-doping laboratory were suspended over the bombshell report.
The officials resigned after President Vladimir Putin called for Russian officials, trainers and athletes to take responsibility for engaging in or abetting doping.
Kamayev had served as RUSADA`s acting director since 2011.
His death came as inspectors from the world athletics` governing body IAAF were due to start a two-day visit to Russia to evaluate anti-doping efforts following a ban for Russian athletes from international competition over the claims.
Kamayev had initially responded defiantly to the WADA report released in November, branding the suspension of Moscow`s anti-doping laboratory "utter nonsense" and ridiculing the allegations as reminiscent of "the epoch of James Bond."
"I have a holster, a pistol, and every day I go to the basements of Lubyanka," he scoffed to journalists in November, using the informal name for the KGB/FSB security service headquarters building in central Moscow.
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