Jailed Kremlin critic Alexei Navalnysaid Tuesday he has been placed in solitary confinement, just weeks after he was transferred to a high-security prison colony in Russias Arctic.Navalny's lawyers found him last month in a special regime colony located in the Yamal-Nenets autonomous district village of Kharp after he disappeared from public view for three weeks.In his first letter since reappearing, the jailed activist said he had undergone an arduous 20-day transfer from a prison in central Russia.As soon as I was released from quarantine [I was given] seven days in SHIZO (Russian for punishment cell), Navalny wrote on X (formerly Twitter).Prison authorities cited Navalnys refusal to follow protocol, respond to educational work and draw proper conclusions for himself as justifications for placing him in solitary confinement, he added.The idea that [President Vladimir] Putin is satisfied by putting me in a barracks in the Far North and Id no longer be tortured with SHIZO was not only faint-hearted but naive, Navalny wrote.The 47-year-old anti-corruption campaigner is serving a 19-year prison sentence on extremism charges that he and his supporters decry as politically motivated.This is Navalnys24th placement in solitary confinement since he was arrested in January 2021 upon returning to Russia, according to the independent news website The Insider.Navalny has spent a total of 273 days in a punishment cell, according to the outlet.Before his transfer, Navalny urged his supporters to vote against Putin in the 2024 presidential election and persuade other Russians to cast ballots for any other candidate.