State prosecutors in Tomsk seek to ban the Russian translation of the Bhagavad Gita, contending it is an extremist religious text that should be on a blacklist that includes Hitler's Mein Kampf.
They said the book spreads "social discord," the IANS news agency reported.
"I consider it categorically inadmissible when any holy scripture is taken to the courts. For all believers these texts are sacred," Russian Ambassador to India Alexander Kadakin said.
He insisted that Russia was a secular and democratic country where all religions enjoyed equal respect.
Kadakin made the statement a day after Indian lawmakers forced an adjournment of parliament over the issue and Hindus staged protests outside the Russian consulate in Kolkata city.
"It is strange that such events are unfolding in Tomsk which is famous for its secularism and religious tolerance," Kadakin said.
"Well, it seems that even the lovely city of Tomsk has its own neighbourhood madmen. It is sad indeed," he added.
The Siberian court is expected to deliver its verdict in the case on December 28.