Americans warned to leave Russia immediately after Putin cops arrest Wall Street Journal reporter Evan Gershkovich

On Thursday, the  once again issued a warning to all Americans living in or travelling to Russia to leave immediately.

Russia has accused Gershkovich of trying to obtain military secrets about a factory - but it has not named the factory and it has so far not provided any evidence to back up its allegation.

The journalist was reportedly held at a restaurant and bundled into a car by plain-clothed officers with a sweater pulled over his head.

He later appeared in court in , where he pleaded not guilty to espionage.

Gershkovich was seen being led into a van by guards from the Lefortovsky court in the Russian capital.

's Kommersant newspaper reports that he will be transported to Moscow's Lefortovo prison, an FSB pre-trial detention facility.

The prison is notorious for its harsh conditions and thousands were shot or tortured to death there during Joseph Stalin's 'Great Terror' of the 1930s, say Russian human rights campaigners.

If convicted, he faces up to 20 years in jail.

He is the first reporter for an American news outlet to be arrested on espionage charges in Russia since the Cold War.

Russia has been accused in the past of arresting Americans to use in barter exchanges for Russians detained in the US.

US basketball star Brittney Griner was held on drug smuggling charges but then swapped for international arms dealer Viktor Bout.

Opponents of Putin, most notably Alexei Navalny, have also found themselves thrown into jail on cooked-up charges.

Gershkovich reports on Russia as part of the Journal’s Moscow bureau and is accredited to work as a journalist in Russia by the country’s foreign ministry, the FSB said.

Fears were raised about Gershkovich when he failed to make contact with his office. 

A spokesperson for the paper said: “The Wall Street Journal is deeply concerned for the safety of Mr. Gershkovich."

It said it "vehemently denies the allegations from the FSB and seeks the immediate release of our trusted and dedicated reporter, Evan Gershkovich".

"We stand in solidarity with Evan and his family," it added.

White House Press Secretary Karine Jean-Pierre said the charges are "ridiculous".

"These espionage charges are ridiculous," Jean-Pierre said.

"The targeting of American citizens by the Russian government is unacceptable."

She said there was no reason to believe the charges were accurate.

His arrest comes amid the bitter tensions between Moscow and Washington over the fighting in Ukraine.

It's understood the US embassy had not been informed about the incident and was seeking information from the Russian authorities about the case.

Russian political analyst Tatiana Stanovaya suggested Gershkovich had been “taken hostage”.

Andrei Soldatov, an author and expert on Russia's security agencies who lives outside the country, came to the reporter's defence.

"Evan Gershkovich is a very good and brave journalist, not a spy, for Christ's sake," he said,

Soldatov said his arrest was a "frontal attack on all foreign correspondents who still work in Russia" adding "and it means that the FSB is off the leash".

Gershkovich's last report from Moscow, published earlier this week, focused on the Russia's economy's slowdown amid Western sanctions imposed when its troops entered Ukraine last year.

The FSB alleged that Gershkovich was acting on US orders to collect classified information about Russia's defence industries.

He was allegedly "engaged in the collection of information about one of the enterprises of the Russian military-industrial complex” which constitute “state secrets”.

Gershkovich was “acting on instructions” from the US government, it was alleged. 

"While trying to obtain secret information, an American was detained in Yekaterinburg,” said the FSB.

However, Putin's spooks have offered no evidence to support the claims.

The Kremlin said that the arrest was "a matter for the FSB" and that it understood that Gershkovich had been "caught red-handed", although again provided no evidence.

Russian reports suggest he had gone to Yekaterinburg to write about the attitude of people to the Ukraine war and the recruitment of locals for the Wagner Group private military company.

The reporter is a US citizen born to parents from the Soviet Union and has lived in Moscow for six years working as a journalist.

Local sources said Gershkovich had made a trip to the city several weeks ago and had returned this week. 

Russia has seldom made allegations of espionage against Western correspondents accredited to the country. 

Many accredited correspondents from Western media outlets left the country when the war 13 months ago started amid concerns it was unsafe to remain.