A Russian judge ruled Tuesday that an American journalist must remain behind bars on espionage charges in a case that is part of a Kremlin crackdown on dissent and press freedom amid the ongoing war in Ukraine.

Appearing in public for the first time in weeks, the 31-year-old Wall Street Journal reporter, Evan Gershkovich, stood in the defendants’ glass cage at Moscow City Court, wearing blue jeans and a navy blue gingham checked shirt. He paced at times with his arms folded, talking through an opening with his lawyers and occasionally smiling as he acknowledged the other journalists crammed into the courtroom.

Mr. Gershkovich is the first American correspondent since the Cold War to be detained in Russia on spying charges, and his arrest rattled journalists in the country and drew outrage in the West. Mr. Gershkovich, his employer, and the American government deny he was involved in spying and have demanded his release.

“Evan is a member of the free press who right up until he was arrested was engaged in newsgathering. Any suggestions otherwise are false,” the Journal has said. Last week, Washington officially declared that Mr. Gershkovich was “wrongfully detained.”

Russia’s Federal Security Service arrested Mr. Gershkovich in the Ural Mountains city of Yekaterinburg on March 29 and accused him of trying to obtain classified information about a Russian arms factory.

In rejecting his appeal to be released from pretrial detention, the judge ruled he must remain in jail until at least May 29. The journalist’s lawyers said they petitioned for a house arrest or for Mr. Gershkovich to be released on bail of about $610,000, but they were rejected.

The Journal and its publisher, Dow Jones, called the ruling upholding Mr. Gershkovich’s detention “disappointing.”

The Department of State has been pressing Moscow to grant consular access to Mr. Gershkovich. The American ambassador to Russia, Lynne Tracy, attended Tuesday’s hearing and said a day earlier that she had visited him in prison. She tweeted that “he is in good health and remains strong,” reiterating the official American call for his immediate release.

Mr. Gershkovich could face up to 20 years in prison if convicted. Russian lawyers have said past espionage investigations took a year to 18 months, during which time he could have little contact with the outside world.

He has been held in Moscow’s Lefortovo prison, which dates from the tsarist era and is a terrifying symbol of repression since Soviet times, used during Stalinist repressions.

“It’s not a very nice place in general, but conditions are okay, he doesn’t complain,” his lawyer, Tatyana Nozhkina, said after Tuesday’s hearing.

Mr. Gershkovich is in good spirits, has no medical complaints, and is exercising and reading a lot, including Leo Tolstoy’s “War and Peace,” she added.

“He’s in good fighting spirit, he’s ready to prove his innocence and defend the media freedom,” she said.

She added that Mr. Gershkovich has received letters from his parents and supporters, but so far hasn’t been allowed any phone calls. He also told his lawyers he was thinking about writing a book about the ordeal when he’s free.

The case comes amid bitter tensions between Moscow and the West over the invasion of Ukraine and as the Kremlin intensifies a crackdown on opposition activists, independent journalists, and civil society groups.

The sweeping campaign of repression is unprecedented since the Soviet era. Activists say it often means the very profession of journalism is criminalized, along with the activities of ordinary Russians who oppose the war.

On Monday, in the same courthouse where Mr. Gershkovich’s hearing was held, the opposition figure Vladimir Kara-Murza was convicted of treason for publicly denouncing the war and sentenced to 25 years in prison. 

President Biden spoke to Mr. Gershkovich’s parents last week and again condemned his detention. “We’re making it real clear that it’s totally illegal what’s happening, and we declared it so,” he said.

The last American reporter to be arrested on espionage charges by Moscow was Nicholas Daniloff in 1986. A correspondent for U.S. News and World Report, Mr. Daniloff spent 20 days in custody before being swapped for an employee of the Soviet Union’s UN mission who was arrested by the FBI, also on spying charges.

A top Russian diplomat said last week that Russia might be willing to discuss a potential prisoner swap with America involving Mr. Gershkovich — but after his trial. That means any exchange is unlikely soon.