Jailed Wall Street Journal reporter Evan Gershkovich has been charged with espionage in Russia and has entered his official denial, Russian state news agency Tass reported Friday.

Tass said a law enforcement source informed the news agency that Russia’s Federal Security Service officially charged the American journalist with espionage. Tass did not specify if the action was taken during a court hearing.

In the Russian legal system, the filing of charges means the formal start of a criminal probe.

Tass quoted its source as saying: “The FSB investigation charged Gershkovich with espionage in the interests of his country. He categorically denied all accusations and stated that he was engaged in journalistic activities in Russia.”

The source declined further comment because the case was considered secret.

Russian authorities arrested Gershkovich last week and accused him of trying to obtain classified information about a Russian arms factory. The Wall Street Journal has denied the accusations.