U.S. economic activity expanded in nine of the country's 12 districts, the Fed said in its Beige Book report of anecdotal information on business activity collected from contacts nationwide.

The Boston Fed described economic activity as upbeat, while the New York and Kansas City districts described it as essentially flat. Most others described activity as modest.

Half the U.S. central bank's districts said the outlook for future economic growth remained mostly positive.

But while the labor market continued to improve and most districts reported "slight to moderate" growth in consumer spending, other sectors showed further strain.

Most manufacturing sectors weakened and "several districts reported the strong dollar's negative impact on demand," the Fed said. Contacts in the Philadelphia and San Francisco districts also cited weak global demand as contributing to declines.

Elsewhere, most areas of the energy sector "struggled further" as oil and gas prices continued to drop. The Cleveland and Kansas districts reported that warmer-than-usual temperatures "increased already abundant inventories of oil and gas and kept downward pressure on already low energy prices."

The Fed raised interest rates last month by a quarter percentage point from near zero, the first hike in almost a decade.

On the whole, Fed policymakers see a further four quarter-point increases in 2016 but have made clear that would depend on incoming data and a tangible move in inflation toward the Fed's 2 percent target.

The report showed little sign the wage pressures that started to tick up in October and November were becoming sustained.

Nearly all districts said overall price pressures were minimal, and just two districts reported an acceleration in wage gains.

"Wage pressures remained relatively subdued," the Fed noted.

The Beige Book was compiled by the Philadelphia Fed with information collected on or before Jan. 4, 2016.