The Federal Prison Service said in a statement that Navalny felt unwell after a walk on Friday and lost consciousness. The politician's team says it has received no confirmation of his death so far.
The death of Russian opposition leader Alexei Navalny in prison was shocking, but hardly surprising. It follows a long line of fallen critics and opponents of Russian leader Vladimir Putin.
The Russian opposition leader was a prominent critic of Vladimir Putin. He was known for organizing nationwide protests against election fraud and government corruption.
In a sign of Navalny's ability to inspire the public, in 2017 his followers chanted words in Putin's hometown that are among the most dangerous to utter in their country: "Russia without Putin."
Associates of the imprisoned Russian opposition leader said Monday that he has been located at a prison colony above the Arctic Circle nearly three weeks after contact with him was lost.
Lawyers of jailed Russian opposition politician Alexei Navalny say they have not been able to confirm his whereabouts for several days, raising concern among his allies for his health and safety.
The Russian activist, a fierce opponent of President Vladimir Putin, was sentenced Friday on extremism charges, which he denies. He is already serving prison sentences on other charges he denies.
Lilia Chanysheva was sentenced to 7 1/2 years in prison in the latest in a series of lengthy prison terms handed down to Kremlin political opponents. Women are increasingly singled out for repression.