Moscow: Moscow has formally charged US journalist Evan Gershkovich with espionage, Russian news agencies reported Friday, adding that he had denied the accusations.

The arrest of Wall Street Journal correspondent Evan Gershkovich prompted an outcry from media outlets and rights groups, as well as government officials in Washington.

"FSB investigators charged Gershkovich with espionage in the interests of his country," Russian state-run agency TASS said, citing a law enforcement source.

"He categorically denied all accusations and stated that he was engaged in journalistic activities in Russia," TASS said.

Gershkovich's arrest is seen as a serious escalation of Moscow's crackdown on the media.

His publication, one of the most prestigious in the United States, "vehemently denies the allegations" against its "trusted and dedicated reporter".

The case has been classified as secret, limiting the amount of information available.

His arrest also comes as Moscow's relationship with Washington has been severely downgraded because of the Ukraine offensive.

Washington has long accused Moscow of arbitrarily arresting Americans in order to secure the release of detained Russians.

US President Joe Biden called for Gershkovich's release on Friday, the White House describing the accusations against him as "ridiculous".

The Democratic and Republican leaders of the US Senate also denounced his arrest.

"We strongly condemn the wrongful detention of US citizen and Wall Street Journal reporter Evan Gershkovich, and demand the immediate release of this internationally known and respected independent journalist," Senate Majority Leader Chuck Schumer and Republican Leader Mitch McConnell said in a rare joint statement.

"Let there be no mistake: journalism is not a crime," the Senate leaders wrote. "We demand the baseless, fabricated charges against Mr. Gershkovich be dropped and he be immediately released."

Schumer and McConnell also reiterated their "condemnation of the Russian government's continued attempts to intimidate, repress, and punish independent journalists and civil society voices."

But Russia said on Thursday it was "pointless" to try to pressure Moscow over the case.

Gershkovich worked for AFP in Russia before taking a job with the Journal.