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Russia's security service said Thursday that it has detained Wall Street Journal reporter Evan Gershkovich, a U.S. citizen, on charges of "espionage in the interests of the American government."

The Russian Federal Security Service (FSB) alleged that Gershkovich "collected information constituting a state secret about the activities of one of the enterprises of the Russian military-industrial complex."

Gershkovich has recently reported on the war in Ukraine and the role played by the Russian paramilitary group Wagner, whose founder told The Daily Beast that he had not heard of the journalist's arrest.

"If you want, I can check the torture cellar in my house to see if he's there," said Yevgeny Prigozhin. "At first glance, I didn't see him among the American journalists I keep there by the dozens. I can, if you want, also look at the fresh graves of foreign journalists on my house plot. But if I'm not mistaken, we didn't bury him there either."

The Journal said in a statement that it "vehemently denies" the accusations against Gershkovich and is pursuing his immediate release. Gershkovich was accredited to work as a journalist in Russia by the nation's foreign ministry.

In response to news of Gershkovich's arrest, the global press freedom group Reporters Without Borders said it is "alarmed by what looks like retaliation: journalists must not be targeted!"