A report released by the Commerce Department suggests the U.S. economy may be strengthening.

According the latest federal data, the economy gained strength at the end of last year as Americans spent at the fastest pace in four years.

The government reports that growth rose to an annual rate of 3.2 percent in October through December. That's up from 2.6 percent in the previous quarter.

Despite the encouraging data, concerns are growing over the threat of a national debt crisis.

Congressional Budget Office Director Doug Elmendorf testified Thursday before the Senate Budget Committee that the U.S. still faces daunting economic and budgetary challenges.

"To prevent debt from becoming unsupportable, Congress will have to restrain spending and raise revenue significantly or pursue a combination of those approaches," he said. "The longer the necessary adjustments are delayed, the greater the consequences of mounting debt."

Elmendorf also said that a return to normal economic conditions would take years.