WASHINGTON — Federal Reserve Vice Chair Janet Yellen says more needs to be done to strengthen the U.S. economy. She made her remarks as Obama nominated her to succeed Ben Bernanke as chair of the nation's central bank.

Yellen said the past six years have been tumultuous for the economy and challenging for many Americans. She said that while the recovery is not complete, quote, "We have made progress, the economy is stronger and the financial system is sounder."

She said considerable credit for the recovery goes to Bernanke. She said it was a privilege to serve with him and learn from him.

Bernanke's term ends Jan. 31. If confirmed by the Senate, Yellen would be the first woman to head the Federal Reserve.