A court in Moscow on Tuesday extended the pretrial detention of an American reporter for The Wall Street Journal by three months, nearly a year to the day after he was detained on accusations of espionage. The United States government has said the charge is politically motivated and unfounded.

The reporter, Evan Gershkovich, 32, was ordered to stay in prison until at least June 30, according to a statement by the news service of the Moscow court system. It was the fifth time that Mr. Gershkovich’s detention had been extended since his arrest in March of last year during a reporting trip. In January, the court extended his detention until March 30.

Mr. Gershkovich, wearing dark denim jeans and a plaid shirt in court, stood with his hands in his pockets and listened to the latest ruling in a courthouse cage, according to a video posted with the statement. A few still images showed Mr. Gershkovich smiling through the glare of the cage. If convicted, he could face up to 20 years in a Russian penal colony.

“This verdict to further prolong Evan’s detention feels particularly painful,” Lynne Tracy, the U.S. ambassador to Russia, said in a statement, noting the anniversary of his arrest. “The accusations against Evan are categorically untrue. They are not a different interpretation of circumstances, they are fiction.”

It can take up to one and a half years for cases like Mr. Gershkovich’s to reach trial. So far, the Russian government has not presented any evidence to support its claims, Ms. Tracy said, “no justification for Evan’s continued detention and no explanation as to why Evan doing his job as a journalist constituted a crime.”

Ms. Tracy said Mr. Gershkovich “has displayed remarkable resilience in strength” during his detention, and she called for his immediate release.

Almar Latour, the publisher of The Wall Street Journal, and Emma Tucker, its editor, said in a statement on Tuesday that they “will continue to do everything in our power to secure his release.”

“The attention and interest around one year is heartening, and we all must be sure to keep Evan front and center for as long as he is wrongfully detained,” they said.

Over the weekend, journalists around the world swam in solidarity with Mr. Gershkovich at 10 different Brighton beaches for the anniversary of his arrest, a tribute to his love of Brighton Beach in Britain and New York.

The Russian authorities have suggested that they could be open to a prisoner swap for Mr. Gershkovich, but only after a verdict is reached in his case.

The U.S. government has designated Mr. Gershkovich “wrongfully detained,” effectively labeling him a political prisoner. Brittney Griner, who was arrested on drug charges and released in December 2022 in a prisoner exchange, and Paul Whelan, a former Marine and corporate executive who is serving a 16-year sentence on espionage charges, also received the designation.

Mr. Gershkovich was the first American journalist to be arrested on a spying charge since the end of the Cold War, highlighting the decaying relationship between Moscow and Washington over Russia’s invasion of Ukraine.

In October, the Russian authorities detained an editor working for Radio Free Europe/Radio Liberty, an American broadcaster funded by the U.S. government. The editor, Alsu Kurmasheva, who holds dual U.S.-Russian citizenship, was charged with failing to register as a foreign agent after going to Russia for family reasons.