ST. PETERSBURG, Russia -- Police in St. Petersburg on Friday found fragments of a 100-year old bas relief depicting the mythical demon Mephistopheles which was removed from the facade of a historic building, in a possible right-wing act of revenge.

The disappearance of the beloved landmark, which overlooked the nearby construction site of a new Orthodox church, raised fears of a growing religious intolerance in Russia. A conservative group on Thursday claimed responsibility for the removing the work of art, saying they set out to eradicate "a cult of Satan."

The St. Petersburg police said on Friday that they have found "fragments of the bas relief" amid construction refuse but it was not clear who took it there.

Prosecutors had opened an investigation into the theft and said they were seeking those suspected of destroying or damaging a cultural heritage object.

Local media reported that a man removed the relief in broad daylight on Wednesday, put it in the back of a truck and drove away.

On Thursday, a group which identified itself as Cossacks of St. Petersburg sent a letter to a popular local news web-site, claiming responsibility.

"It is odd that an image of devil hung outside the church and made it difficult for the cross to be installed," the letter published by Fontanka.ru said. "We were indignant that this awful legend, outrageous story was used as a tourist trap, became a point of pride, like an open reverence of Satan."

The Cossack community in St. Petersburg, however, denied that its members could be behind the attack. Andrei Polyakov, community chief, said the Cossacks of St. Petersburg simply "does not exist."

The disappearance has sparked outrage in the city which was Russia's capital from the 18th century until 1918 and remains Russia's cultural hub, hosting such prominent art collections as the Hermitage.

The theft follows a flurry of attacks by ultra-conservative activists against modern art in Russia.

Earlier this month, several activists ransacked an exhibition of Soviet-era non-conformist artists just outside the Kremlin, shouting that the works were offensive to Christians.

The same group which said it was behind the removal of Mephistopheles claimed responsibility for spray-painting "pedophile" on the family home of Russian-American novelist Vladimir Nabokov in St. Petersburg in 2013.