The U.S. Federal Reserve should expand its holdings of mortgage bonds and Treasury securities until the central bank is satisfied with the health of the economy, Eric Rosengren, president of the Federal Reserve Bank of Boston, told the New York Times.

"You continue to do it until you have documented evidence that you're getting growth in income and the unemployment rate consistent with your economic goals," Rosengren told the NY Times in an interview.

Rosengren said several indicators, including the unemployment rate and the share of the population in the work force, had retreated to their levels at the beginning of the year.

"For the last seven months we've been treading water. That's different from what we expected at the beginning of the year. I think it's time to swim to shore," he told the newspaper.

However, Richard Fisher, president of the Dallas Federal Reserve and a consistent hawk on monetary policy, told Reuters in an interview that the real problem with the economy, and the stubbornly high jobless rate, was Congress's lack of action on fiscal policy.

Fisher said he had no doubt the Fed would in theory be able to push down mortgage rates further with more purchases of housing-backed bonds, but that doing so likely wouldn't bring down unemployment.

A government jobs report released on Friday showed the jobless rate ticked up to 8.3 percent in July.