The Kremlin said on Tuesday that Wall Street Journal reporter Evan Gershkovich had "violated Russian law" and been caught "red-handed," one day after the U.S. State Department officially designated him as having been "wrongfully detained."
Russia's federal security service arrested Gershkovich last month on espionage charges widely decried as bogus by the White House, other Western countries, the Wall Street Journal, dozens of media organisations and human rights groups.
The United States' determination that he was "wrongfully detained" means it believes he was targeted primarily because he is an American citizen, and its transfer of the case from the State Department to the office of the Special Envoy for Hostage Affairs raises the issue's political profile.
"We're making it real clear that it's totally illegal what's happening and we declared it, so -- changes the dynamic," U.S. President Joe Biden told reporters.
Gershkovich's family said later they had spoken with Biden.
"We are encouraged that the State Department has officially designated Evan as wrongfully detained. We appreciate President Biden's call to us today, assuring us that the U.S. government is doing everything in its power to bring him home as quickly as possible," the family said in a statement.
Asked about the State Department's move, Kremlin spokesman Dmitry Peskov repeated Russia's position that Gershkovich broke the law.
He said Gershkovich had "been caught red-handed and violated the laws of the Russian Federation", before adding: "This is what he's suspected of, but of course, the court will make a decision".
More than 99% of criminal cases in Russia end in a conviction and the country has long been criticised by rights monitors for a lack of judicial independence.
Russia has presented no evidence to support the case against Gershkovich, which is proceeding in secret because Russia says the case materials are confidential.
Next week, a court will hear an appeal from Gershkovich's legal team against an order that he be held in pre-trial detention at Moscow's Lefortovo prison until May 29.
Another detainee, Paul Whelan, was allowed to speak to his parents on Monday for the first time in 12 days and was aware of Gershkovich's case, his brother David said.
Whelan, a former Marine who has been held in Russia since 2018, was not included when the United States secured the release of basketball star Brittney Griner in exchange for arms dealer Viktor Bout in December.
"Paul's fear of being left behind a third time was apparently palpable in his conversation with our parents yesterday," David Whelan said in a statement. "It would be an unconscionable betrayal."
(Reporting by Reuters; Editing by Gareth Jones, David Ljunggren, Jonathan Oatis and Mark Heinrich)