There's a purge of spies underway in Moscow, where two high-ranking Russian security service agents, a cybersecurity expert and a fourth man have been charged with treason for passing along secrets to American intelligence, according to a lawyer defending one of the men.
The men were charged "with treason in favor of the United States," said Ivan Pavlov, the lawyer for one of the defendants.
So far, the counterintelligence raid is targeting computer security professionals -- men once trusted with Russian government secrets about hacking operations.
The crackdown comes shortly after the U.S. intelligence officials in October officially accused Russia of using hackers to try steering the presidential election to Donald Trump. American officials have never stated that Russian government insiders gave them information that led to that accusation.
Several national experts, who do not have direct knowledge of American intelligence operations, suspect that Russian government insiders did leak information and that this Russian crackdown is a result of that.
Russia's Interfax news agency, which quoted anonymous sources, said both FSB officers are accused of passing confidential information to the CIA.
However, other media reports in Russia, also quoting unnamed sources, claim these men have been arrested for taking part in a hacking ring that targeted Russian officials.
The two government agents were arrested in December and were officials in the FSB -- the nation's top security agency that was once known as the KGB. One was Sergei Mikhailov, head of the FSB Information Security Centre. The other was his deputy, Dmitry Dokuchayev. Russian media outlets have been reporting the treason charges in recent days, citing anonymous sources.
Russian security teams also arrested an employee of Russian internet security firm Kaspersky Lab. Ruslan Stoyanov was the head of the company's computer incidents investigation team, where he oversaw hacking investigations.
In a statement, Kaspersky said he was under investigation "for a period predating his employment at Kaspersky Lab." He had joined the company in July 2012, according to his LinkedIn profile. Kaspersky also insisted it has "no political ties to any government."
Pavlov would not disclose the identity of his client, the fourth man arrested. Pavlov told CNN that the charges against his client include providing help to "several special services of the United States."
Under Article 275 of the Russian Criminal Code, treason is punishable by 12 to 20 years in prison.
The Kremlin has declined to confirm any details of the case. U.S. officials would not comment on the reported arrests.
Several American security experts, including those formerly employed by the U.S. National Security Agency, fear for the safety of these prisoners.
Paul Rosenzweig, once the Department of Homeland Security's deputy assistant secretary for policy, recently speculated that these men could be killed for providing information to the United States.
"Their blood may be on our hands," Rosenzweig wrote last week in a widely read national security blog.
CNN's Evan Perez and Simon Ostrovsky contributed to this report.