Switzerland's secretive banks currently hold up to $213 billion of Russian wealth, the country's financial industry association has announced, as sanctions on Russia allow a rare insight into Swiss vaults.

According to the Swiss Bankers Association (SBA), the banks have between 150 billion and 200 billion Swiss francs ($213 billion) of Russian client money in offshore accounts.

The extent of wealthy Russians storing their money in Switzerland, one of the world's most attractive hubs for offshore accounts, is much more extensive than previously thought, now that several of its financial firms have begun to detail their accounts in light of the sanctions.

The SBA's revelation is rare for Switzerland, which has blocked many previous transparency requests on its banking system, and follows an equally unusual decision to mirror the majority of EU sanctions on Russian money amid Moscow's military operation against Ukraine.

The conflict has sparked a renewed Swiss public debate over transparency, with Mattea Meyer, co-president of the Social Democrats, calling for Switzerland to further target any money belonging to Russians tied to the Kremlin. 

"Part belongs to oligarchs loyal to the Kremlin. The money and their activity ... helps finance the war," she said, adding that Switzerland "must do everything possible to turn off the money taps".

The SBA estimate, much higher than initial indications of the credit exposure to Russia, also shows the scale of the challenge in implementing the unprecedented sanctions and its potential effect on Swiss finance. 

However, it stressed that this was small compared to overall assets held in Switzerland, which has been regarded by generations of wealthy individuals from around the world as a safe haven for their money.

"The share of assets held for Russian clients likely accounts for a share in the low single-digit percentage range of the total cross-border assets deposited with Swiss banks," it said.

Switzerland's two biggest banks last week detailed "limited" exposures to Russia, with the largest UBS saying a $634 million direct exposure had been cut since year-end. 

Credit Suisse said Russian money accounts for around 4 percent of the assets overseen by Switzerland's second-biggest bank, amounting to tens of billions of dollars. 

But amid Western sanctions against Russia, banks are seeing their business with Russian clients fall under much closer scrutiny, with UBS and other Swiss banks declining to detail assets they hold for Russian customers.

UBS CEO Ralph Hamers said the bank was not only looking to shield against current compliance but also against the risk of future penalties, adding that the sanctions were keeping Switzerland's biggest bank busy.