The Federal Reserve isn't yet convinced that the U.S. economy's growth can accelerate on its own.
That was the message Fed officials sent Wednesday, when they reinforced their plan to keep short-term interest rates at record lows at least until unemployment falls to 6.5 percent.
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"We are seeing improvement," he said. "One thing we would need is to see this is not temporary improvement."
The Fed will continue buying $85 billion a month in bonds indefinitely to keep long-term borrowing costs down. Bernanke said the Fed might vary the size of its monthly purchases depending on whether or how much the job market improves. The unemployment rate has fallen to a four-year low of 7.7 percent, among many signs of a healthier economy.
The Fed's statement took note of the global stresses that have been intensified by the turmoil in Cyprus, which is trying to stave off financial ruin. No longer does the Fed statement say, as it did in January, that "strains in global financial markets have eased somewhat."
Bernanke was asked at the news conference whether the flare-up in Cyprus signals that the U.S. financial system might be more vulnerable than bank "stress tests" have shown. Bernanke said that "at this point" he sees no major risks to the U.S. financial system or economy.
The Fed noted in its statement that the U.S. job market has improved, consumer spending and business investment have increased and the housing market has strengthened. But its latest economic forecasts, also released Wednesday, show that the Fed still doesn't expect unemployment to reach 6.5 percent until 2015.
The Fed also cautioned that government spending cuts and tax increases could slow the economy. It predicts that growth won't exceed 2.8 percent this year, slightly lower than its December forecast of 3 percent.