The head of the U.S. central bank says the economy is growing more slowly than expected.

U.S. Federal Reserve Chairman Ben Bernanke Wednesday that the slower growth is due to temporary problems such as the disruptions caused by Japan's earthquake and an increase in gasoline prices.

The Fed's experts now expect around 2.8 percent growth this year, which is about four-tenths of a percentage points lower than earlier estimates.

In a meeting with journalists, Bernanke also said unemployment is declining from its current 9.1 percent, but at a “frustratingly” slow pace. The Fed predicts the jobless rate will fall as low as 7 percent in 2013.

The economic assessment comes after two days of consultations among top bank officials and follows several disappointing economic reports.

Fed officials voted to keep interest rates steady in the ultra-low range where they have been for some time.