Wall Street Journal reporter Evan Gershkovich was arrested on espionage charges on Tuesday, and his detention was extended by a Moscow court until January 30, according to Russian news agencies.

The criminal case against the American reporters is classified, according to the authorities, which is why the hearing was held behind closed doors.

The 32-year-old Gershkovich was arrested in March while visiting Yekaterinburg, a Russian city located roughly 2,000 kilometers (1,200 miles) east of Moscow, for reporting purposes. The reporter “gathered information constituting a state secret about the activities of one of the enterprises of the Russian military-industrial complex,” according to the Russian Federal Security Service, “acting on the instructions of the American side.”

The claims are refuted by Gershkovich and the Journal, and the US government says he was wrongfully detained. The charges of espionage have not been substantiated by any evidence provided by Russian authorities.

Since Nicholas Daniloff, a Moscow correspondent for U.S. News and World Report, was detained by the KGB in 1986, Gershkovich is the first American journalist to face espionage charges in Russia. He is being held at the notoriously harsh Lefortovo prison in Moscow.

As tensions between the United States and Russia increased after Russia sent troops into Ukraine, analysts have noted that Moscow may be using American prisoners as negotiating chips. In exchange for Russians imprisoned in the United States, at least two American citizens, including WNBA player Brittney Griner, were detained in Russia in recent years.

According to the Russian Foreign Ministry, Gershkovich’s swap will only be taken into consideration following the outcome of his trial. Espionage trials in Russia can drag on for over a year.

Wall Street Journal reporter Gershkovich’s detention is being extended by a Russian court until the end of January.