Two Russian banks governed by three billionaire friends of President Vladimir Putin have been hit hard by sanctions in the US.
Assets worth some $647m have now been frozen across the country.
The banks Rossiya and SMP are among the dozens of Russian companies hit by sanctions as a result of the crisis in Ukraine.
Washington and the EU have imposed several rounds of sanctions against Moscow since the conflict in Ukraine began.
President Obama recently announced the strategy against Russia will continue until the end of 2015.