Federal Reserve Chairman Ben S. Bernanke said he would not rule out further bond purchases to boost growth and reduce unemployment, which he called a “grave concern.”

“The costs of nontraditional policies, when considered carefully, appear manageable, implying that we should not rule out the further use of such policies if economic conditions warrant,” Bernanke said today in a speech to central bankers and economists at an annual forum in Jackson Hole, Wyoming.

Bernanke's speech comes two weeks before he leads a meeting of the Federal Open Market Committee to decide whether an expansion of the Fed's record stimulus is needed to spur growth. Two rounds of large-scale asset purchases totaling $2.3 trillion have so far failed to reduce the jobless rate below 8 percent more than three years into the recovery.