Russian authorities have detained politician Yevgeny Roizman known for his criticism of the Kremlin and, more recently, of the military campaign in Ukraine, Russia's TASS news agency reported on Wednesday.
Roizman, a former mayor of the city of Yekaterinburg, is being investigated for "discrediting the Russian army", TASS reported, citing Yekaterinburg security services.
Roizman was one of a handful of Kremlin critics who won mayoral posts following a series of big opposition demonstrations as President Vladimir Putin campaigned for office in 2012.
Russia calls its actions in Ukraine a "special military operation" aimed at ensuring its own security and authorities have prosecuted a number of activists for calling it a war or criticising Russia's action.
Ukrainian forces have mounted stiff resistance and the West has imposed sweeping sanctions on Russia in an effort to force it to withdraw its forces.