Russia's detention of an American correspondent for The Wall Street Journal on espionage charges is certain to worsen Moscow's diplomatic feud with Washington over the war in Ukraine and likely to further its isolation.

Evan Gershkovich's arrest marks the first time a U.S. reporter has been detained on spying accusations since the Cold War.

The newspaper denied the allegations and demanded the immediate release of "trusted and dedicated reporter."

The White House said the State Department was in direct contact with the Russian government over Gershkovich's detention and urged U.S. citizens living or travelling in Russia to depart immediately.

"These espionage charges are ridiculous. The targeting of American citizens by the Russian government is unacceptable," White House Press Secretary Karine Jean-Pierre said at a news briefing.

In a statement, Secretary of State Antony Blinken connected the detention to the crackdown on media in Russia, whose relations with Washington have nosedived since the invasion of Ukraine.

"In the strongest possible terms, we condemn the Kremlin's continued attempts to intimidate, repress, and punish journalists and civil society voices," Blinken said.

Gershkovich, a 31-year-old who has worked in Russia as a journalist for six years, is the highest-profile American arrested there since basketball star Brittney Griner, who was freed in December after 10 months in jail on drugs charges.

Gershkovich was detained in the city of Yekaterinburg while allegedly trying to obtain classified information, the Federal Security Service, known by the acronym FSB, said Thursday.

The service, which is the top domestic security agency and main successor to the Soviet-era KGB, alleged that Gershkovich "was acting on instructions from the American side to collect information about the activities of one of the enterprises of the Russian military-industrial complex that constitutes a state secret." It did not identify the complex.

Gershkovich was brought to Moscow, where a court at a closed hearing ordered him held in pre-trial detention until May 29.

Gershkovich, who has been working for the Journal for just over a year, told the court he was not guilty. His employer said the case against him was based on a false allegation.

Gershkovich, who covers Russia, Ukraine and other ex-Soviet nations as a correspondent in the Journal’s Moscow bureau, could face up to 20 years in prison if convicted of espionage.

Prominent lawyers noted that past investigations into espionage cases took a year to 18 months, during which time he may have little contact with the outside world.

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

Kremlin spokesperson Dmitry Peskov told reporters: "It is not about a suspicion, it is about the fact that he was caught red-handed."

Gershkovich speaks fluent Russian and had previously worked for the French news agency Agence France-Presse (AFP) and The New York Times. He was a 2014 graduate of Bowdoin College in Maine, where he was a philosophy major who cooperated with local papers and championed a free press, according to Clayton Rose, the college's president.

Zakharova said Russia would grant the U.S. consular access to Gershkovich, adding that the case against him would be made public.

Daniil Berman, a lawyer representing the reporter, was not permitted inside the courtroom or allowed to see the charges, he told reporters outside. He believed Gershkovich would be taken to Lefortovo, the 19th-century central Moscow jail notorious in Soviet times for holding political prisoners.

The 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."

Rossiya-24 state TV ran a segment of nearly five minutes on Gershkovich's arrest about 17 minutes into its 6 p.m. bulletin.

Its correspondent said Gershkovich's work had an "openly propagandist character," citing as evidence a story carrying his byline this week that was headlined "Russia's Economy is Starting to Come Undone."

The Russian TV report noted that the Yekaterinburg region where he was detained is a major hub of Russia's defense industry, suggesting this was the object of his "curiosity."

The arrest comes at a moment of bitter tensions between the West and Moscow over its war in Ukraine and as the Kremlin intensifies a crackdown on opposition activists, independent journalists and civil society groups.

The case could further isolate Russia by scaring off more of the few foreign journalists still working there.

Moscow has effectively outlawed all independent Russian news outlets since the start of the war but has continued to accredit some foreign reporters.

Journalism has become sharply limited by laws that impose long sentences for any public criticism of the war, which Russia refers to as a "special military operation."

The sweeping campaign of repression is unprecedented since the Soviet era. Activists say it often means the very profession of journalism is criminalized, along with the activities of ordinary Russians who oppose the war.

Earlier this week, a Russian court convicted a father over social media posts critical of the war and sentenced him to two years in prison. 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.

Daniloff was released without charge 20 days later in a swap for an employee of the Soviet Union’s United Nations mission who was arrested by the FBI, also on spying charges.

Gershkovich's last report from Moscow, published earlier this week, focused on the Russian economy's slowdown amid Western sanctions imposed after Russian troops invaded Ukraine last year.

Ivan Pavlov, a prominent Russian defense attorney who has worked on many espionage and treason cases, said Gershkovich's case is the first criminal espionage charge against a foreign journalist in post-Soviet Russia.

"That unwritten rule not to touch accredited foreign journalists, has stopped working," said Pavlov, a member of the First Department legal aid group.

Pavlov said the case against Gershkovich was built to give Russia "trump cards" for a future prisoner exchange and will likely be resolved "not by the means of the law, but by political, diplomatic means."

Russian Deputy Foreign Minister Sergei Ryabkov said it was too early to talk of any possible prisoner swap with the United States, saying that such deals are typically arranged only after a prisoner is convicted.

"I wouldn't even consider this issue now because people who were previously swapped had already served their sentences," Ryabkov said, according to Russian news agencies.

In December, WNBA star 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.

"Our family is sorry to hear that another American family will have to experience the same trauma that we have had to endure for the past 1,553 days," Whelan’s brother David said in an emailed statement.

"It sounds as though the frame-up of Mr. Gershkovich was the same as it was in Paul's case."

Jeanne Cavelier, of the press freedom group Reporters Without Borders, said Gershkovich's arrest "looks like a retaliation measure of Russia against the United States."

"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," said Cavelier, head of the Eastern Europe and Central Asia desk at the Paris-based group.

Russian journalist Dmitry Kolezev said on Telegram that he spoke to Gershkovich before his trip to the Ural Mountain city of Yekaterinburg, Russia’s fourth-largest, about 1,670 kilometers (about 1,035 miles) east of Moscow.

"He was preparing for the usual, albeit rather dangerous in current conditions, journalist work," Kolezev wrote.