The U.S. economy is at increasing risk of becoming trapped in a prolonged phase of slow growth that points to the need for lower interest rates than previously expected, Federal Reserve policymaker Jerome Powell was quoted as saying.

Powell, a member of the Federal Reserve Board of Governors, told the Financial Times he favored a "very gradual" path for any rises as U.S. economic outlook was dogged by global risks.

"The probability of an era of weaker growth, lower potential growth - that worries me more than it used to," he was quoted as saying in Monday's edition of the newspaper.

"With inflation below target, I think we can be patient."

Powell spoke on Thursday, the day before strong U.S. nonfarm payrolls numbers for July led to markets ramping up bets on a U.S. rate rise this year.