Tens of thousands of people gathered in cities across Russia's far-eastern Khabarovsk region on Saturday, demanding the release of their governor.
A Moscow court on Friday ordered Sergei Furgal to be held in pre-trial detention for two months.
Furgal was detained a day earlier in connection with several murders and attempted murders of entrepreneurs in 2004 and 2005. He has pleaded innocent to the charges.
Supporters of the governor took to the streets, shouting: "Shame on Moscow," "Putin's a thief," and "Down with the tsar," in references to President Vladimir Putin.
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Others carried signs with the slogans: "I Am Sergei Furgal" and "Free Furgal."
Observers in the city of Khabarovsk spoke of the biggest protest in years, reported the German press agency.
The AFP news agency said tens of thousands of people took part in the Khabarovsk march.
Similar but smaller rallies took place in Komsomolsk-on-Amur, Elban, Solnechny, and other cities in the region.
The demonstrations were largely peaceful and there were no arrests, reported local media.
"We are sure you will be heard," the governor's spokesperson Nadezhda Tomchenko told demonstrators via Instagram.
Politically motivated arrest?
Standing as a candidate for the nationalist Liberal Democratic Party of Russia (LDPR), Furgal became governor of the Khabarovsk region that borders China in 2018.
He won 70% of the vote, beating the long-time incumbent and Russia's ruling United Russia Party candidate, Vyacheslav Shport.
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Furgal is considered the "organizer of the attempted murder and the murder of a number of business people," said Russia's Investigative Committee in a statement.
The LDPR denounced the arrest: "This is a very big political case," said LDPR leader Vladimir Zhirinovsky, following Furgal's arrest on Thursday.
Zhirinovsky accused the government of using "methods from the Stalinist era."
Kremlin spokesperson Dmitry Peskov dismissed these claims as "unmeasured" and "fundamentally untrue."
Two further LDPR lawmakers were arrested on Friday on fraud charges.
They will be held in custody until September, reported Radio Free Europe, citing a district court representative.
kmm/mm (AFP, dpa)