U.S. stocks are closing lower, extending losses from last week.
The price of crude oil continued to drop Monday, and Russia's ruble plunged to a record low against the dollar.
The Dow Jones industrial average fell 100 points, or 0.6 percent, to 17,180.
The Standard & Poor's 500 index fell 12 points, or 0.6 percent, to 1,989. The Nasdaq composite lost 48 points, or 1 percent, to 4,605.
Russia's ruble plunged 13 percent against the dollar. The falling price of oil, which is the chief source of Russian exports and tax revenue, has weighed heavily on the currency.