A court in Moscow has extended the detention of Wall Street Journal reporter Evan Gershkovich, arrested on espionage charges, until Jan. 30, Russian news agencies reported. The hearing took place on Tuesday behind closed doors because authorities say details of the criminal case against the American journalist are classified.

Gershkovich was detained in March while on a reporting trip to the Russian city of Yekaterinburg. Russia’s Federal Security Service alleged that the reporter, “acting on the instructions of the American side, collected information constituting a state secret about the activities of one of the enterprises of the Russian military-industrial complex”.