MOSCOW — Increasingly jittery over all forms of public protest, Russian security forces on Thursday cut short a trek of thousands of miles to Moscow by a Siberian shaman who has been walking for six months on a mission to drive President Vladimir V. Putin and “demonic” forces from the Kremlin.

The Interior Ministry in Buryatia, a region in eastern Siberia, said in a statement that the shaman, Aleksandr Gabyshev, had been detained because he was wanted for “committing a crime” in his home region of Yakutia and would be sent there for questioning by investigators.

It did not specify what this alleged crime was or explain why, if Mr. Gabyshev had indeed been wanted for months, it took so long to pick him up even as supporters regularly publicized his whereabouts on YouTube.

Amnesty International protested the shaman’s arrest and called for his release, saying that he had been “abducted by a squad of masked law enforcement officials and held in an undisclosed location.”