Mumbai: French financial group Societe Generale, which has acquired a 20-per cent stake in OAO Rosbank, has filed a request with Russia''s antitrust authorities to exercise call option worth about $1.7 billion to take control of the Russian banking group.

The acquisition was made at a record-high premium, with a price-to-equity ratio of 5.9.

The option gives La Defense-based Societe Generale , France''s No.2 bank, the right to buy a 30-per cent stake in Rosbank, which would boost its holding in the Russian lender to 50 per cent plus one share.

The stake would further rise to 58 per cent as a result of a requirement to buy out a handful of minority shareholders.

"We have asked the antitrust authorities for permission to exercise the option," said Societe Generale spokeswoman Stephanie Carson-Parker. "After that we will ask the central bank for their permission and then we will decide if we will go ahead."

Societe Generale has until the end of 2008 to decide whether to buy the additional stake.

Societe Generale, one of the largest banks in the euro zone, has been at the forefront of a pack of western banks looking eastward at Russia''s fast-growing and retail banking sector.

Moscow-based Rosbank is one of the largest privately owned banks in Russia, operating about 650 outlets, including 67 branches, in the majority of the country''s regions.

Other western acquisition in Russia''s banking sector include Belgium''s KBC Group NV''s April agreement to buy a majority stake in Moscow-based Absolut Bank in a deal worth €761 million, while in January Italy''s UniCredit SpA agreed to pay France''s VTB Bank SA $395 million for 20 per cent of International Moscow Bank.