Outgoing Federal Reserve Chair Janet Yellen offered an upbeat assessment of the US economy on Wednesday, saying the growth rate has picked up the pace in recent months.

She reaffirmed that the Fed expects to raise interest rates only gradually. However, she steered clear of signaling a rate hike at the December policy meeting, which her designated successor, Jerome Powell, offered on Tuesday.

"The US economy has strengthened further this year," despite the impact of two late summer hurricanes, Yellen said in testimony before the Joint Economic Committee of Congress. "Economic growth appears to have stepped up from its subdued pace early in the year."