Russian police are arresting protesters demanding the release of top Russian opposition leader Alexei Navalny at demonstrations in the country’s east.

Larger unsanctioned rallies are expected later Saturday in Moscow and other major cities.

Navalny, who is President Vladimir Putin’s most prominent and durable foe, was arrested on January 17th when he returned to Moscow from Germany, where he had spent five months recovering from a severe nerve-agent poisoning that he blames on the Kremlin.

Authorities say his stay in Germany violated terms of a suspended sentence in a criminal conviction in a case that Navalny says was illegitimate.

Activists say at least 48 people were detained in cities including Vladivostok and Khabarovsk.