Russian opposition leader Alexei Navalny has been missing for six days, his spokesperson said Monday.
Navalny press secretary Kira Yarmysh wrote on X, formerly Twitter, that Navalny did not appear in court Monday for a scheduled appearance and has not been heard from in the past six days.
Yarmysh said she and other Navalny supporters “don’t know where Alexei is or what’s happening to him.”
White House national security spokesperson John Kirby said the U.S. was “deeply concerned” about the reports that Navalny was missing.
“He should be released immediately. He should never have been jailed in the first place,” Kirby told reporters. “We’re going to work with our embassy in Moscow to see how much more we can find out.”
Navalny has been imprisoned since 2021 on a nine-year sentence for fraud and contempt of court charges. He was also sentenced to an additional 19 years earlier this year for extremism charges.
The Kremlin critic is one of the chief political opponents of Russian President Vladimir Putin.
Navalny has accused Putin of corruption for more than a decade and runs an activist organization, the Anti-Corruption Foundation, which works from exile in Lithuania.
From prison, the opposition figure has continued to call for revolution and protests against Putin and has spoken out against Russia’s invasion of Ukraine.
Navalny was last heard from last week, when he released an online statement pushing for voters to oppose Putin in the 2024 elections, who he said will try to rig the election.