Russia's dollar-denominated RTS stock exchange index dropped 4.51 percent compared to the previous close, while the country's ruble-denominated MICEX index fell 4.43 percent at closing on Wednesday.
As of 18:45 Moscow time, the RTS index amounted to 1,537.57, the MICEX to 1,431.41.
The Russian stock market joined the panic on international trading floors on Friday when S&P took the decision to cut the U.S. top rating by one notch to AA-plus over concerns of America's growing budget deficit.
Late on Tuesday, the U.S. Federal Reserve System announced a decision to keep its key rate unchanged at close to zero for two more years, which led to slight stabilization on the stock markets in mid-day but rapid drop continued in the evening.
The European stocks accelerated their decline following a negative open of the U.S. trading and the announcement the country's wholesale statistics appeared to be lower than analysts forecast.
As of 18:30 Moscow time, the Dow Jones index fell by 3.65 percent to 1,0829.2, S&P 500 dropped by almost 4 percent to 1,126.23, Nasdaq by 3.45 percent to 2,396.76.