The Federal Security Service said Thursday that Gershkovich was detained in the Ural Mountains city of Yekaterinburg while allegedly trying to obtain classified information.

The FSB, which is the top successor agency to the Soviet-era KGB, alleged that Gershkovich “was acting on the U.S. orders to collect information about the activities of one of the enterprises of the Russian military industrial complex that constitutes a state secret.”

“The Wall Street Journal vehemently denies the allegations from the FSB and seeks the immediate release of our trusted and dedicated reporter, Evan Gershkovich,” the newspaper said. “We stand in solidarity with Evan and his family.”

The arrest comes amid bitter tensions between the West and Moscow over its war in Ukraine and as the Kremlin intensifies its crackdown on opposition activists, independent journalists and civil society groups. The broad government campaign of repression hasn’t been seen since the Soviet era.

Earlier this week, a Russian court convicted a single father over social media posts critical of the war in Ukraine and sentenced him to two years in prison while his 13-year-old daughter was sent to an orphanage.

Gershkovich is the first American reporter to be arrested on espionage charges in Russia since September 1986, when Nicholas Daniloff, a Moscow correspondent for U.S. News and World Report, was arrested by the KGB. He was released without charges 20 days later in a swap for an employee of the Soviet Union’s United Nations mission who was arrested by the FBI.

The FSB didn’t say when the arrest took place. Gershkovich, who covers Russia, Ukraine and other ex-Soviet nations as a correspondent in the Wall Street Journal’s Moscow bureau, could face up to 20 years in prison if convicted of espionage.

The FSB noted that he had accreditation from the Russian Foreign Ministry to work as a journalist, but ministry spokeswoman Maria Zakharova said Gershkovich was using his journalistic credentials as a cover for “activities that have nothing to do with journalism.”

Gershkovich speaks fluent Russian and had previously worked for the French agency Agence France-Presse and The New York Times. His last report from Moscow, published earlier this week, focused on the Russian economy’s slowdown amid Western sanctions imposed when Russian troops invaded Ukraine last year.

Gershkovich’s arrest follows a swap in December, in which WNBA star Brittney Griner was freed after 10 months behind bars in exchange for Russian arms dealer Viktor Bout.

Another American, Paul Whelan, a Michigan corporate security executive, has been imprisoned in Russia since December 2018 on espionage charges that his family and the U.S. government have said are baseless.

Jeanne Cavelier, head of Eastern Europe and Central Asia desk at the Paris-based press freedom group Reporters Without Borders, said Gershkovich was the first foreign journalist who was arrested in Russia since the start of the war in Ukraine.

“It looks like a retaliation measure of Russia against the United States, so we are very alarmed because it is probably a way to intimidate all Western journalists that are trying to investigate aspects of the war on the ground in Russia,” Cavelier she told The Associated Press. “The Western powers should immediately ask for clarifications on the charges, because as far as we know he was just doing his job as a journalist.”

Russian journalist Dmitry Kolezev said on the messaging app Telegram that he spoke to Gershkovich before his trip to Yekaterinburg.

“He was preparing for the usual, albeit rather dangerous in current conditions, journalist work,” Kolezev wrote. He said Gershkovich asked him for the contacts of local journalists and officials in the area as he prepared to arrange interviews.