"The transaction with Roberto Cavalli was implemented by VTB Capital's business division, which is responsible for providing consulting services to our clients," the source said on condition of anonymity.
"VTB Group continues to actively develop its international operations in line with the existing business strategy," it added.
According to the Russian business daily Vedomisti, VTB Capital wants to buy a 60-percent stake in the fashion house known for exotic prints and sand-blasted jeans.
The stake's €500 million ($670 million) price values Roberto Cavalli at €830 million, Vedomisti cited a trade journal as saying.
VTB Capital, which says it is not directly affected by EU sanctions, declined to confirm the report when contacted by AFP.
Cavalli's fashion house also declined to comment.
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The 73-year-old designer has sought to sell part or all of his company for several years.
The Bahreini investment fund Investcorp reportedly discussed a price of €450 million, while the Financial Times said a comparable level had been mulled by the European fund Permira.