A shaven-headed Evan Gershkovich appeared briefly before journalists in a Russian court on Wednesday at the start of a trial on charges of espionage.
Gershkovich, 32, was seen standing in a glass box, wearing an open-necked shirt and with his arms folded.
The Wall Street Journal reporter is accused by prosecutors of gathering secret information on the orders of the US Central Intelligence Agency about a company that manufactures tanks for Russia's war in Ukraine. If convicted, he faces a sentence of up to 20 years.
He, his newspaper and the US government all reject the allegations and say that he was just doing his job as a reporter accredited by Russia's Foreign Ministry to work there.
The proceedings will take place behind closed doors, meaning that the media is excluded and no friends, family members or US embassy staff are allowed in to support Gershkovich. Such arrangements are common at spying or treason trials in Russia.
Against the background of the Ukraine war, Gershkovich and other Americans detained in Russia have been caught up in the gravest crisis between Moscow and Washington for more than 60 years.
President Vladimir Putin has said Russia is open to the idea of a prisoner exchange involving Gershkovich and that contacts with the United States have taken place, but they must remain secret.
The US has accused Russia of conducting "hostage diplomacy". It has designated Gershkovich and another jailed American, Paul Whelan, as "wrongfully detained" and says it is committed to bringing them home.
