U.S. ambassador to Russia Lynne Tracy said she found journalist Evan Gershkovich "in good health" when meeting him in prison Monday for the first time after his arrest on spying charges.
"I visited The Wall Street Journal's Evan Gershkovich today at Lefortovo Prison — the first time we've been permitted access to him since his wrongful detention more than two weeks ago," the embassy quoted her as saying on Twitter.
"He is in good health and remains strong," she added.
Gershkovich is due to appeal his detention on Tuesday.
The American has been charged with espionage and faces up to 20 years in prison.
Moscow accuses him of trying to obtain classified defense information for the U.S. government.
The reporter, The Wall Street Journal and U.S. officials vehemently deny the allegations.
His case is classified, which limits the information available to the public.
On Tuesday, President Joe Biden called Russia's imprisonment of the Wall Street Journal journalist "totally illegal" and told his family he was working to secure his release.
Russian Deputy Foreign Minister Sergei Ryabkov last week reiterated Russia's stance that any exchanges could only be decided after a court delivers a verdict.