"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.

"Russian President Vladimir Putin has promised to protect Bank Rossiya. 'I personally don't have an account there, but I certainly will open one on Monday,' he told a meeting of Russia's Security Council."