About 316,000 people filed for first-time unemployment benefits, up 19,000 from the previous week's revised figure. Economists had expected a slight drop in claims to 295,000.
The last time there were more people filing jobless claims was the first week of September.
But the weekly data can be volatile, and last week's jump could be caused by complications related to adjusting for the end of many seasonal holiday jobs.
The less-volatile four-week average was 298,000 last week. That was an increase of 6,750 from the previous week.
Initial claims have been running below 300,000 in recent months, a level indicating a healthy labor market. The figures have been consistent with the economy's strong job growth.
The U.S. added 252,000 net new jobs in December, and the unemployment rate fell to a six-year low of 5.6%.
Job growth last year was the best since 1999, and economists expect the improvements to continue. Federal Reserve policymakers are watching labor-market indicators closely to determine when to start raising rock-bottom interest rates.