FILE PHOTO: The Russian flag flies on the dome of the Kremlin Senate building in Moscow

MOSCOW (Reuters) -Russia has charged a jailed American citizen with espionage, state news agencies reported, upping the pressure on U.S. President Joe Biden's administration which has been trying to find a way to bring several detained citizens back home from Russia.

Russia's RIA and TASS news agencies said that Moscow's Lefortovo court had remanded Gene Spector in pre-trial custody on suspicion of espionage, which is punishable with a jail term of 10 to 20 years.

"The court granted the request of the investigation to detain a U.S. citizen Spector on charges under Article 276 (espionage) of the Criminal Code of the Russian Federation," TASS quoted an unidentified source at the court as saying.

The news agencies did not report any details of the new charges, but said the court session was held behind closed doors as the case materials were classified.

Spector is already serving a 3-1/2-year sentence after pleading guilty to his role in bribing an assistant of ex-Russian Deputy Prime Minister Arkady Dvorkovich, according to the news agencies.

Spector was born in what is now St. Petersburg and then moved to the United States. Before his 2021 arrest, he served as chairman of the board of Medpolymerprom Group, a company specialising in cancer-curing drugs, TASS said.

Speaking on CNN, White House spokesperson John Kirby said the administration was still collecting information about the case and had no comment yet.

A State Department spokesperson said they were aware of reports of charges against a U.S. citizen in Russia and were monitoring the situation, but declined to comment further.

The United States has been talking to Russia about ways to bring back several American citizens detained in Moscow, including Wall Street Journal reporter Evan Gershkovich and former U.S. Marine Paul Whelan.

The Kremlin has confirmed that it has held some discussions with Washington but has repeatedly said swaps can only be considered after trials and has cautioned that U.S. attempts to speak publicly about the talks will undermine efforts.

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Russia's ambassador to the United States, Anatoly Antonov, said on Wednesday that Moscow and Washington operate an effective channel to swap prisoners.

The Journal's Gershkovich was arrested in March on espionage charges that he, the Journal and Washington deny. Russia says he was caught red handed.

Former U.S. Marine Whelan is serving a 16-year sentence in a Russian penal colony after being convicted of espionage charges that Washington also says are a sham. U.S. Secretary of State Antony Blinken spoke by phone to Whelan this month.

Last December, U.S. basketball star Brittney Griner was released in a prisoner swap, having been sentenced to nine years in a penal colony for possessing vape cartridges containing cannabis oil - which is banned in Russia - after a judicial process labelled a sham by Washington.

Since the war in Ukraine began in February 2022, the United States has repeatedly told its citizens to leave Russia due to the risk of arbitrary arrest or harassment by Russian law enforcement agencies.

In June, Michael Travis Leake, a U.S. musician and former paratrooper, was shown in court, locked in a metal cage. He was arrested on drug dealing charges. Reuters was unable to reach him for comment.

Brazil this year refused a U.S. request to extradite Sergey Cherkasov, who Western intelligence agencies say is a Russian spy who tried to use a false identity to infiltrate the International Criminal Court (ICC).

(Reporting by Maxim Rodionov, Kanishka Singh and Lidia Kelly; additional reporting by Simon Lewis; Editing by Daniel Wallis, Raju Gopalakrishnan, Nick Macfie and Jonathan Oatis)