Stocks are closing sharply lower as tensions flare up over Russia's presence in Ukraine.
The Dow Jones industrial average fell 231 points, or 1.4 percent, to close at 16,108 Thursday, its worst loss in six weeks.
The Standard & Poor's 500 index fell 21 points, or 1.2 percent, to 1,846. The Nasdaq composite fell 62 points, or 1.5 percent, to 4,260.
U.S. and European leaders have been stepping up their rhetoric against Moscow ahead of a weekend vote in Crimea over whether to secede from Ukraine and join Russia.
Secretary of State John Kerry warned Russia that it will face "very serious" steps from the U.S. and Europe if it annexes Crimea.
Bond prices rose as traders sought safety. The yield on the 10-year Treasury note fell to 2.65 percent.