The yield on the 10-year Treasury rose to 2.35 percent, its highest in 15 months. The Dow Jones industrial average fell more than 200 points.
"Any whiff there's going to be reduction in the (Fed's) ammunition is met with selling," said James Camp, managing director of fixed income at Eagle Asset Management.
The Fed has been buying $85 billion worth of bonds each month to keep long-term rates low, and stimulate the economy. On Wednesday, the Fed sketched a brighter outlook for the economy and Chairman Ben Bernanke said the bank's purchases could slow.
Rates have already risen significantly since May 3, when the yield on the 10-year hit its lowest point of the year, 1.63 percent. Investors have been pushing up those rates in anticipation of the day when the central bank stops buying bonds.
If rates rise too fast, investors can get spooked.
"You want a nice, gradual rise," said Talley Leger, a strategist at Macro Vision Research. "But when it's furious and disorderly like today, it's too fast. It can have a negative impact on stocks."
A brighter outlook for the U.S. economy normally would convince people to buy stocks, not sell them. But Leger said investors have become hooked on Fed stimulus and sold.
"Markets are asking for expansion of already stimulative policies, and they're not getting it," he said. "It's like a drug supplier and an addict."
The stock market drifted lower for most of the day, ahead of a scheduled statement from the Fed and a press conference by Bernanke.
The Standard & Poor's 500 index was down about half a percentage point shortly after the Fed released its statement. Then Bernanke said at the news conference that the Fed could scale back its bond purchases later this year, and the selling accelerated. The index ended the day down 22.88 points, or 1.4 percent, to 1,628.93.
Bonds and stocks both slumped even though Bernanke said that the central bank was in no hurry to raise rates and would only cut back on its stimulus once the economy had improved sufficiently.
"There is going to be some nervousness as we adjust to a more normal economic environment," said Brad Sorensen, director of market and sector research at Charles Schwab. "Both the stock and bond markets are adjusting to a Federal Reserve that isn't going to have the spigots wide open."
The yield on the five-year Treasury note also rose sharply. It jumped to 1.23 percent from 1.06 percent late Tuesday. The 5-year yield also hit its lowest level of the year, 0.65 percent, on May 3.
The yield on the 30-year bond rose to 3.42 percent from 3.34 percent Wednesday.
An index measuring the dollar against six other currencies surged 1 percent. The dollar rose against the Japanese yen, the euro and other currencies as traders anticipated higher U.S. rates.
