Master and Visa cards are closed to Russians
The US says Bank Rossiya has links to senior Russian officials
Visa and MasterCard have blocked credit card services to some Russian bank customers as a result of US sanctions.
Four banks are so far affected, all of which have links to Russians blacklisted by the US.
Visa and MasterCard, both US-based companies, are forbidden from having any dealings with those targeted by the sanctions.
The banks, which said card services stopped without warning, have described the move as unlawful.
One of the banks affected, Bank Rossiya, is described by the US as Russia's 15th largest, with assets of $12bn (£7.27bn).
The St Petersburg-based bank has been singled out by Washington as the personal bank for senior Russian officials. US officials said it would be "frozen out" from the dollar.
Russian President Vladimir Putin said Bank Rossiya had nothing to do with events in Crimea and promised to transfer his wages there.
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