Federal Reserve Chair Janet Yellen said on Monday the U.S. central bank's "extraordinary" commitment to boosting the economy, especially the still struggling labor market, will be needed for some time to come.

Yellen, in her first public speech since becoming Fed chair two months ago, strongly defended the Fed's policies of low interest rates and continued bond-buying. Citing the struggles of three American workers as examples, she said there remains "considerable" slack in the economy and job market, a sign that further monetary stimulus can still be effective.

"I think this extraordinary commitment is still needed and will be for some time, and I believe that view is widely shared by my fellow policy-makers at the Fed," Yellen said at the 2014 National Interagency Community Reinvestment Conference.

The Fed, frustrated with the slow recovery from the 2007-2009 recession, has kept rates near zero for more than five years. It has said it will keep them there for a considerable time even after it ends a bond-buying program, which is to be wound down later this year.

In a speech that sounded political at times, Yellen, long concerned with the hardships of the unemployed and under-employed, said the U.S. economy remains "considerably short" of the Fed's goals of maximum sustainable employment and stable inflation at 2 percent.

The "scars from the Great Recession remain, and reaching our goals will take time," she told about 1,100 people gathered at a downtown convention center here. "The recovery still feels like a recession to many Americans, and it also looks that way in some economic statistics."