US President Barack Obama applauds after announcing his nomination of Janet Yellen to head the Federal Reserve at the White House in Washington October 9, 2013. If confirmed, Yellen will run the world's most influential central bank, providing some relief to markets that would expect her to tread carefully in winding down economic stimulus. The nomination puts Yellen on course to be the first woman to lead the institution in its 100-year history. [Photo/Agencies]

President Barack Obama nominated Federal Reserve Vice Chair Janet Yellen on Wednesday to run the world's most influential central bank and urged the Senate to confirm her without delay.

Yellen, an advocate for aggressive action to stimulate U.S. economic growth through low interest rates and large-scale bond purchases, would replace Fed Chairman Ben Bernanke, whose second term ends on January 31.

The nomination will put Yellen on course to be the first woman to lead the institution and the first to head a central bank in any Group of Seven industrial nation.

"Janet is exceptionally well qualified for this role," Obama said at a White House ceremony, with a beaming Yellen standing by his side. "She doesn't have a crystal ball, but what she does have is a keen understanding about how markets and the economy work, not just in theory but also in the real world. And she calls it like she sees it."

If confirmed by the U.S. Senate, which is expected to endorse her despite opposition from some Republicans, Yellen would provide continuity with policies under Bernanke. She would likely move cautiously in reining in monetary stimulus put in place to shore up the world's largest economy.

Yellen, who spoke briefly after Obama, said she would promote maximum employment, stable prices, and a sound financial system.

She said there was more to do to ensure people who were out of work can find jobs.

"While we have made progress, we have farther to go. The mandate of the Federal Reserve is to serve all the American people, and too many Americans still can't find a job and worry how they'll pay their bills and provide for their families," Yellen said.

"The Federal Reserve can help if it does its job effectively."

While she spoke, the president stood close by her side, looking at her attentively. When she was done, he clasped her hand warmly and put his hand on her shoulder, applauding as they left the room together with Bernanke.

Expectations that the Fed might start to taper its stimulus program have been a concern for financial markets since May. The central bank shocked investors in September by maintaining its cash injections of $85 billion a month in full.

Yellen's nomination coincides with a political stalemate in Washington that has partially closed the U.S. government and threatened a U.S. default if lawmakers fail to raise the country's $16.7 trillion debt ceiling by an October 17 deadline.