Allies of imprisoned opposition politician Alexei Navalny sounded the alarm when they discovered he was no longer in the prison where he had been serving his time and there was no word on where he had been taken.
But late in the day, the chairman of a prison monitoring commission said Navalny had been transferred to a maximum-security prison nearby.
Navalny was moved to the IK-6 prison in the village of Melekhovo in the Vladimir region, Russian news agencies reported, citing Sergei Yazhan, chairman of the regional Public Monitoring Commission. Melekhovo is about 250km east of Moscow.
Prison transfers in Russia sometimes take days and are shrouded in secrecy. The lack of information about the whereabouts of Navalny, the most determined political foe of Russian President Vladimir Putin, had worried his allies.
"All this time we don't know where Alexei is. He is left alone with the system that has already once tried to kill him," Navalny's spokeswoman, Kira Yarmysh, said earlier on social media. After the transfer was reported, she said his close associates had not been able to independently confirm it.