Federal Reserve Chairman Ben Bernanke says the U.S. economy has shown improvement in recent months, but that the Fed won't alter its aggressive stimulus policies until it is convinced the gains can be sustained.

Federal Reserve Bank Chairman Ben Bernanke (Chip Somodevilla/Getty Images)

During a news conference Wednesday after the Fed's two-day policy meeting, Bernanke repeated that the Fed plans to keep its key short-term interest rate near zero until the unemployment is below 6.5 percent. But he said that's a "threshold," not a trigger."

He also said the central bank may vary the size of its monthly bond purchases depending on improvement in the job market. It is currently spending $85 billion a month to help lower long-term rates.

"We are seeing improvement," Bernanke said. "One thing we would need is to see this is not temporary improvement."


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