The Federal Reserve's latest signals on interest rates gave U.S. stocks a lift for much of Wednesday, but the rally didn't last.

A sell-off in the final minutes of trading knocked the Dow Jones industrial average and the Standard & Poor's 500 index slightly into the red. The slide extended a three-day losing streak for the two indexes. Only the Nasdaq composite held its course, carving out a slight gain.

Materials and energy stocks were among the biggest decliners as U.S. crude oil prices declined again.

Investors were mostly focused on Fed Chair Janet Yellen's remarks on the economy and interest rates as she delivered her semiannual report to Congress.

The market has been anxious about the possibility of interest rate hikes at a time when the global economy is showing signs of slowing. But Yellen's remarks addressed investors' concerns, said Erik Davidson, chief investment officer for Wells Fargo Private Bank.

"The markets have gotten the message that the Fed is not on autopilot," Davidson said. "If they'd gotten the sense that the Fed was on autopilot and was predestined to a certain number of rate hikes in 2016, that would have been troublesome."

The Dow fell 99.64 points, or 0.6 percent, to 15,914.74. The average is now down 8.7 percent this year. The S&P 500 index slipped 0.35 point, or 0.02 percent, to 1,851.86. The index is off 9.4 percent this year.

The Nasdaq added 14.83 points, or 0.4 percent, to 4,283.59. The gain helped trim the Nasdaq's losses for the year, which stand at 14.5 percent.

Investors appeared to be in a buying mood early in the day in anticipation of Yellen's testimony. That sent stocks higher early on and sustained them until the last-minute slide as oil prices closed lower.

Benchmark U.S. crude fell 49 cents, or 1.8 percent, to close at $27.45 a barrel in New York. Brent crude, a benchmark for international oils, rose 52 cents, or 1.7 percent, to close at $30.84 a barrel in London.

Yellen offered no major surprises in prepared remarks released before the start of her two-day Congressional testimony. She reiterated the Fed's confidence that the U.S. economy was on track for stronger growth and a rebound in inflation.

At the same time, she cautioned that global weakness and falling financial markets could depress the U.S. economy's growth. That would, in turn, slow the pace of Fed interest rate hikes, she said.

Yellen also made clear that the central bank won't likely find it necessary to cut rates after having raised them from record lows in December.

Since the Fed decided to raise its key interest rate from a record low in December, the U.S. economy has hit some turbulence and markets have become volatile. Traders are increasingly worried about a number of issues, including the fall in the price of oil to multi-year lows, a slowdown in China and whether many parts of the global economy will fall into recession and suffer a debilitating period of deflation, or falling prices.

A delay or slower rollout of interest rate increases by the Fed is seen as good for the market, as higher interest rates can be detrimental to stocks, Davidson said.

"Higher interest rates can be detrimental to equities, although we're of the view that we're not at risk of higher interest rates in the short term," Davidson said.

All told, eight of the 10 sectors in the S&P 500 index declined, with materials and energy stocks posting the biggest drops. Health care and technology stocks bucked the downward trend.

Akamai Technologies notched the biggest increase in the S&P 500 index, surging 21.2 percent. It added $8.39 to $47.96. Assurant fell the most. The stock lost $10.26, or 13.4 percent, to $66.23.

Several big media companies slumped.

Disney dropped 3.8 percent a day after it reported that its ESPN network has hit a soft patch. The stock was the biggest decliner in the Dow, sliding $3.47 to $88.85. Time Warner was down 5 percent after its revenue fell short of forecasts. Time Warner shed $3.14 to $60.07.

In Europe, Germany's DAX added 1.6 percent, while France's CAC 40 rose 1.6 percent. Britain's FTSE 100 gained 0.7 percent. In Asia, Japan's Nikkei 225 sank 2.3 percent and is down about 11 percent in the past month. Australia's S&P/ASX 200 shed 1.2 percent. Markets were closed in China, Taiwan, Hong Kong and South Korea for Lunar New Year holidays. Hong Kong and Korea reopen on Thursday and China and Taiwan resume trading on Monday.

Precious metals prices closed lower. Gold fell $4, or 0.3 percent, to $1,194.60 an ounce and silver slid 17 cents, or 1.1 percent, to $15.28 an ounce. Copper, an industrial metal that will often rise and fall along with investor's optimism about the global economy, fell 1 cent, or 0.6 percent, to $2.03 a pound.

Bond prices rose. The yield on the 10-year Treasury slipped to 1.67 percent from 1.73 percent late Tuesday. The dollar fell to 113.68 yen from 115.01 yen, while the euro rose to $1.1277 from $1.1287 the day before.

In other energy trading in New York, wholesale gasoline rose 4 cents, or 4.9 percent, to 94 cents a gallon and home heating oil was flat at 97 cents a gallon. Natural gas fell 5 cents, or 2.5 percent, to $2.05 per 1,000 cubic feet.