The ruble declined for a 10th day against the Central Bank's target dollar-euro basket, extending its longest losing streak since January 2009, as oil prices fell after the Federal Reserve said there are "significant downside risks" to the U.S. economy.

The ruble depreciated more than 0.9 percent to 37.04 versus the basket as of 6:59 p.m. in Moscow on Thursday, the weakest level since December 2009. The ruble sank about 1.7 percent to 32 against the dollar and was little changed at 43.05 against the euro.

Russian stocks sank on Thursday, with the 30-stock MICEX Index down 7.8 percent to 1,389.43 by the 6:45 p.m. close in Moscow, its sharpest retreat since February 2009. The RTS Index lost 8.6 percent to 1,387.86.