President Joe Biden on Thursday said he’s serious about pursuing a prisoner exchange for a Wall Street Journal reporter who has been detained in Russia for more than 100 days.

The Kremlin earlier this month suggested that it was open to a possible prisoner exchange that could involve Evan Gershkovich, but it underscored that such talks must be held out of the public eye.

Speaking at a news conference in Helsinki, Finland, Biden made clear that the U.S. is interested.

“I'm serious on a prisoner exchange,” Biden said. “That process is underway."

Gershkovich was arrested on espionage charges in the city of Yekaterinburg while on a reporting trip. He is being held at Moscow’s Lefortovo prison, notorious for its harsh conditions. A Moscow court recently upheld a ruling to keep him in custody until Aug. 30.

Gershkovich and his employer deny the allegations, and the U.S. government has declared him to be wrongfully detained. His arrest rattled journalists in Russia. Authorities there have not provided any evidence to support the espionage charges.