The number of Americans filing applications for unemployment benefits shot up last week by the largest amount in 16 months, reversing two weeks of big declines.

The Labor Department reported Thursday that 325,000 newly laid-off workers filed claims for jobless benefits last week, an increase of 36,000 from the previous week. That was the biggest one-week rise since a surge of 96,000 claims the week of Sept. 10, 2005, when devastated Gulf Coast businesses laid off workers following Hurricane Katrina.

The increase of 36,000 was bigger than the 20,000 rise that had been forecast. Analysts, however, cautioned that it is difficult to read the claims figures at this time of year because of unusually wide swings caused by the holidays and other factors.

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