U.S. sanctions aimed at hitting Russia's financial industry appear to be having an impact.

Three Russian banks reported Friday that Visa (V) and MasterCard (MA) cards were not working for the banks' customers.

Western financial institutions are reacting to U.S. sanctions designed to punish some of the top people in Russian President Vladimir Putin's inner circle.

The sanctions ban transactions with several named individuals, and one of the banks -- Bank Rossiya.

MasterCard said it stopped offering card services at three Russian banks -- Bank Rossiya, Sobinbank and SMP Bank -- in accordance with the sanctions. Other operations in Russia continue normally, it said.

Sobinbank is a subsidiary of Rossiya, and SMP Bank is controlled by two of the named individuals.

Visa was not available for comment.

Russian oligarchs, banks and corporations have borrowed heavily from the West, underscoring the risks for both sides in escalating the Ukraine crisis.

Total Russian foreign debt stood at $732 billion at the end of 2013, up by nearly $200 billion over two years. Russian companies continue to tap Western finance but analysts say banks may become wary about taking on new business given the risk of more far-reaching sanctions in the future, or retaliation by Moscow.

"Foreign investors may anticipate further official action and restrict Russian entities' access to external financing," noted ratings agency Fitch. "In a worst-case scenario, the US may prevent foreign financial institutions from doing business with Russian banks and corporates."

Several European and U.S. banks declined to comment on whether they were changing their approach to Russia.

Bank of America (BAC), Deutsche Bank (DB) and ING (ING) said they would honor any U.S. sanctions.

"It is our long-standing policy to comply with any official U.S. government sanction against any country or individual, and we will do so in this case," Bank of America said in a statement.

Deutsche Bank said: "We are following developments and will apply any sanctions, if appropriate, as directed by the relevant authorities."

Related: U.S. sanctions on Russia begin to bite

U.S. banks have lent relatively little to Russia, at just $37 billion, or about 0.25% of assets, according to data from the Bank for International Settlements.

Bank of America called its $6 billion in credit exposure to Russia "modest", compared to its total exposure of more than $1.9 trillion.

European bank lending to Russia is much larger, at $184 billion, or 0.4%, of total banking industry assets.

French banks have lent the most, with a total of $51 billion, followed by Italy, Germany, the U.K. and the Netherlands. Austria is also significantly exposed, relative to the size of its banking sector.

Economists at Deutsche Bank said foreign financial institutions could suffer if Russia decided to freeze assets in retaliation for sanctions, or if the creditworthiness of Russian borrowers declined as a consequence of an escalation in the crisis.

But the risks to the European banking sector would be tightly concentrated in a small number of banks. "Lending outside the euro area is not an operation on which 'bread and butter' institutions would easily embark," they said.

The sanctions are part of a strategy by the West to exert pressure on Russia for annexing Crimea.