A sell-off on Wall Street gained momentum into the close Wednesday on rising worries over North Korea and comments that the Fed could start pulling back on its stimulus program this summer.
Earlier in the day, a weaker-than-forecast report about private sector job growth and sluggish growth in the services sector weighed on stocks.
North Korea threat: Investors were rattled after the Department of Defense announced that it was sending a land-based missile defense system to Guam to defend against possible North Korean ballistic missile launches.
Speaking at the National Defense University, Defense Secretary Chuck Hagel said North Korea presents "a real and clear danger and threat" to the United States.
"We are doing everything we can, working with the Chinese, others, to defuse that situation on the peninsula," said Hagel.
Fed ready to end bond buying? Investors also took a step back after San Francisco Federal Reserve Bank president John Williams said that if the economy improves, as he suspects it will, the Fed could start tapering its bond purchase program.
Williams said he expects to continue seeing a substantial improvement in the job market by this summer.
"If all goes as hoped, we could end the purchase program sometime late this year," Williams said, speaking in Los Angeles.
The Fed's stimulus measures, including its commitment to low interest rates and several rounds of bond buying, have been largely credited for fueling the stock market rally.
All about jobs: Payroll processing firm ADP reported Wednesday that the U.S private sector added 158,000 jobs in March. That was weaker than expected and comes just days ahead of the government's closely watched monthly jobs report.
On Friday, the Labor Department is slated to release the March jobs report ahead of the opening bell. Analysts expect the economy to have added 192,000 jobs last month, according to Briefing.com.
Meanwhile, the Institute for Supply Management's monthly report on growth in the service sector was also disappointing. The ISM Services index came in at 54.4 for March, marking the weakest pace of growth in seven months.
What's moving: Shares of Zynga ( shot up almost 15% after the online gaming firm announced it would soon ) launch its first real money games -- ZyngaPlusPoker and ZyngaPlusCasino -- in the U.K..
Monsanto ( shares rose after the company's profit and earnings topped expectations on strong sales of its biotech seeds. )
Shares of ConAgra ( declined after the food producer said its quarterly profit tumbled 57% due to costs associated with its acquisition of Ralcorp. )
J.C. Penney's ( shares edged lower. The company disclosed late Tuesday that it had ) slashed the pay of CEO Ron Johnson and other executives as the retailer continues to struggle.
Tesla ( shares dropped more than 7% as investors were underwhelmed by the electric car maker's announcement of )a new financing option for buyers.
The dollar declined against the euro, the British pound and the Japanese yen.
Oil and gold prices dropped more than 1%.
The price on the 10-year Treasury yield rose, pushing the yield down to 1.81% from 1.86% late Tuesday.