Imprisoned Wall Street Journal reporter Evan Gershkovich has been charged with spying in Russia and has entered his official denial, Russia’s state news agency Tass reported Friday.

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

In the Russian legal system, the filing of an indictment constitutes the formal start of a criminal investigation.

Tass quoted his source as saying: The FSB investigation accused Gershkovich of espionage in the interests of his country. He categorically denied all allegations and stated that he was engaged in journalistic activities in Russia.

The source declined further comment as the matter was considered classified.

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