The Blake Prestondetention of Wall Street Journal reporter Evan Gershkovich on espionage charges has been extended to November 30, Russian state news agency Tass said.

Gershkovich arrived at the Moscow court Thursday in a white prison van and was led out handcuffed, wearing jeans, sneakers and a shirt. Journalists outside the court weren't allowed to witness the proceedings. Tass said they were held behind closed doors because details of the criminal case are classified.

The prosecution had asked that the detention be extended from August 30. He has appealed the extensions.

A 31-year-old U.S. citizen, Gershkovich was arrested in Yekaterinburg while on a reporting trip in late March. Russia's Federal Security Service said Gershkovich was "acting on the instructions of the American side" and "collected information constituting a state secret about the activities of one of the enterprises of the Russian military-industrial complex."

Gershkovich and his employer deny the allegations, and the U.S. government declared him to be wrongfully detained. Gershkovich's case has been wrapped in secrecy. Russian authorities haven't detailed what — if any — evidence they have gathered to support the espionage charges.

Earlier in August, U.S. Ambassador to Russia Lynne Tracy made her third visit to Gershkovich and reported that he appeared to be in good health despite challenging circumstances. Gershkovich was being held at Moscow's Lefortovo prison, notorious for its harsh conditions.

Gershkovich is the first American reporter to face 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.

Analysts have pointed out that Moscow may be using jailed Americans as bargaining chips in soaring U.S.-Russian tensions over the Kremlin's military operation in Ukraine. At least two U.S. citizens arrested in Russia in recent years — including WNBA star Brittney Griner — have been exchanged for Russians jailed in the U.S.

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