WASHINGTON, April 29 (Reuters) - Federal Reserve Chair Jerome Powell said that he will leave the U.S. central bank when "I think it's appropriate to do so," and said that this reflects his concern about the series of legal attacks on the Fed that threaten its ability to conduct monetary policy.

"I worry that these attacks are battering the institution and putting at risk the thing that really matters to the public, which is the ability to conduct monetary policy without taking into consideration political factors," Powell told a news conference after his last policy meeting as chair.

He said it was important for Americans to be able to depend on a central bank free of political influence.

"It's part of the absolute foundation of this amazing economy that we have. It's just one of the many reasons why the U.S. economy is the envy of the world," Powell said, adding that his decision was not about verbal criticism from elected officials.