NEW YORK >> Warnings of weaker sales from two major companies and concern that the Federal Reserve could pull back its support for the economy sent the stock market spiraling lower Thursday.

Before the start of trading, Wal-Mart cut its estimates for annual revenue and profit, warning that cautious shoppers are spending less. The news followed a revenue forecast from Cisco Systems late Wednesday that was weaker than Wall Street expected.

The Standard & Poor’s 500 index was down 20 points, or 1.2 percent, to 1,666 at noon Eastern Daylight Time.

The selling swept across all 10 industry groups in the index, and 93 percent of the index’s 500 stocks fell.

The Dow Jones industrial average lost 177 points, or 1.2 percent, to 15,159. The Nasdaq composite index fell 52 points, or 1.4 percent, to 3,618.

“It seems like an overreaction today,” said Randy Frederick, managing director of active trading and derivatives at the Schwab Center for Financial Research.

Frederick said many investors are speculating that the improving economy means the Fed will start pumping less money into the financial system in the coming months. If that results in lower bond prices and higher yields, it could lead more investors to dump dividend-paying stocks in favor of bonds.

“Some of the stocks getting hit hardest recently are big companies paying dividends,” Frederick said. Utilities stocks are down 3 percent this week, for example, the worst of the S&P 500’s industry groups.

The government said early Thursday that the number of Americans applying for unemployment benefits dropped to 320,000 last week. That’s the lowest level since October 2007, two months before the start of the Great Recession.

Wal-Mart fell $1.50, or 2 percent, to $74.92, after the world’s largest retailer cut its profit and revenue expectations for 2013. It reported second-quarter results that missed Wall Street’s estimates.

Cisco Systems announced plans to cut 5 percent of its workforce, roughly 4,000 employees, as sales slow. CEO John Chambers called the global economy “challenging and inconsistent.” Cisco plunged $1.88, or 7 percent, to $24.50.

Cisco’s announcement weighed on other technology stocks, as it’s widely regarded as a bellwether for the entire industry. That’s because the company sells a wide range of products to corporations and governments and its fiscal quarters end a month later than most major technology companies, which gives investors an early look into current conditions.

Major stock indexes have slumped more than 1 percent for the week. The Dow is down 1.7 percent and the S&P 500 1.5 percent.

The stock market had been on a tear this year, reaching all time-highs on Aug. 2. The Dow is still up 16 percent in 2013; the S&P 500 up 17 percent.

In the market for U.S. government bonds, the yield on the 10-year note jumped to 2.79 percent, the highest level since July 2011.

Higher long-term interest rates hit real-estate stocks, because the yield on the 10-year U.S. government bond is a benchmark for interest rates on mortgage loans. A sharp increase in mortgage rates could cool demand for new houses and squelch a recovery in the housing market.

Equity Residential lost 1.21, or 2 percent, to 51.35, while Kimco Realty Corp. 51 cents or 2 percent to $21.22.