More than a thousand Russians have rallied in St Petersburg after a century-old bas relief of a mythical demon was destroyed amid fears of increasing religious intolerance under President Vladimir Putin.
The figure of Mephistopheles was last week ripped down from the facade of a century-old building in St Petersburg.
An obscure group calling itself the Cossacks of St Petersburg claimed responsibility.
The seemingly religiously-motivated act of vandalism caused an outcry in the former imperial capital and police launched a probe.
The figure of a bat-winged creature on Lakhtinskaya Street dated back to around 1910.
By some accounts, the bas relief paid homage to legendary Russian opera singer Feodor Chaliapin famed for his role of Mephistopheles.
More than a thousand people including architecture preservationists gathered in front of the building in the city centre on Sunday to express their dismay over what activists dubbed a "brazen act of vandalism".
"Hands off art," read one placard, while another one said in English: "Save our St Petersburg".
"What happened is awful," said Anna Astakhova, 35.
"If it's true that the bas relief was destroyed for religious reasons, then we are descending into the Middle Ages. This is inadmissible."
In an open letter, the Cossacks of St Petersburg said the figure encouraged "open worship of Satan" and was unacceptable because it was opposite a church.
Established Cossack groups in the city denied any knowledge of this group, however.
Police said they had found smashed fragments of the figure in rubbish sacks.
Prosecutors have opened a probe into destruction of cultural heritage, which carries a jail term of up to two years.
Since 2012 Putin has been promoting an unflinchingly conservative agenda in a move aimed at cementing his support among blue-collar workers and elderly Russians.
Kremlin critics say that after the seizure of Crimea from Ukraine last year that conservative trend has become disturbingly strong.