President Joe Biden on Friday called for Russia to release Wall Street Journal reporter Evan Gershkovich, who is being held on espionage charges, while rebuffing a call from the paper's editorial board to expel Russian journalists from the United States.

Asked by White House reporters what his message was to Russia regarding Gershkovich, a US citizen, Biden said: "Let him go."

The Wall Street Journal's board of opinion editors called in a piece published Thursday afternoon for the expulsion of Russia's ambassador to the United States, as well as "all Russian journalists working here," describing the move as "the minimum to expect."

"The timing of the arrest looks like a calculated provocation to embarrass the US and intimidate the foreign press still working in Russia," it added.

The Journal's editor in chief, Emma Tucker, sent a note to the newspaper's staff Friday, saying that "we will carry on doing everything in our power to secure Evan's release."

"Your safety and security are what matters most to me, and we will continue to protect that no matter where you may be reporting from," she added.

Speaking to reporters before leaving to view tornado damage in Mississippi, Biden said that expelling Russian journalists was "not the plan right now."

Gershkovich is believed to be the first foreign journalist held for spying in post-Soviet Russia, and his arrest is expected to escalate the Kremlin's confrontation with the West amid Moscow's war in Ukraine.

Kremlin spokesman Dmitry Peskov, responding to the editorial board's demand that all Russian journalists be expelled, said "the newspaper can say that, but it should not happen. There's just no reason for this."

He said that Gershkovich had been caught "red-handed."

- 'Secret' case -

According to Russian state news agency TASS, Gershkovich denied the charges against him at a court hearing in Moscow. He was remanded in custody until May 29 pending trial.

The case has been classified as "secret", TASS reported, which restricts information that can be published about it.

The only details available are that Russia's security agency announced it had "foiled an illegal activity" by arresting Gershkovich in Yekaterinburg -- about 1,100 miles (1,800 kilometers) east of Moscow -- on an unspecified date.

The 31-year-old journalist's detention, on charges that carry a maximum penalty of 20 years behind bars, is a serious escalation of Moscow's sweeping crackdown on the media.

The White House condemned the arrest and warned Americans not to travel to Russia, while also advising those now inside the country to leave for their own safety.

"The targeting of American citizens by the Russian government is unacceptable. We condemn the detention of Mr. Gershkovich in the strongest terms," White House Press Secretary Karine Jean-Pierre said in a statement.

US officials said they were in touch with the family of Gershkovich as well as the newspaper and that the State Department had contacted Russia.

Several other US citizens are in jail including Paul Whelan, a former Marine, who was arrested in 2018 and handed a 16-year sentence on espionage charges that he denies.