U.S. Secretary of State John Kerry told Russian President Vladimir Putin that he may "find himself with asset freezes on Russian business." There are also talks of boycotting the Group of Eight summit of leaders in the Olympic host city of Sochi this summer.
BNY Mellon's Russia ADR Index slumped 9 percent Monday morning, and is now down more than 27 percent for the year. Stocks in the index include metals company Mechel, which fell 7 percent to $1.76; Russia's biggest mobile communications operator, Mobile Telesystems, tumbled 9 percent at $15.60. Another mobile phone company, VimpelCom, is off 7 percent to $9.44.
In addition, U.S.-traded shares of Yandex, Russia's biggest Internet search engine, fell 13 percent to $32.49.
Global markets were shaken by the developments in Ukraine and Crimea, as fears of contagion spread. A number of Europe's biggest banks fell sharply.
Russia essentially took control of Crimea, a Ukrainian peninsula with strategic importance, and the new Ukrainian government in Kiev fears a wider invasion. The West responded by questioning Russia's membership in the Group of Eight leading industrialized democracies, and the U.S. threatened possible asset freezes and trade penalties.
In Moscow, the Russian stock market dropped about 10 percent and the ruble - already down nearly 10 percent this year - fell to its lowest point ever against the dollar and the euro.
Russia's central bank decided to temporarily increase its key interest rate by 1.5 percentage points, to 7 percent, in a bid to keep the ruble's fall from driving up inflation.
Markets also fell elsewhere in Europe. In the U.S., the Standard & Poor's 500 index dipped 12 points, or 0.7 percent, to 1,847 as of 11 a.m. Eastern time.