First-time claims for unemployment benefits fell 6,000 last week to 422,000 and productivity growth slowed to 1.8 percent in the first quarter, the U.S. Labor Department said Thursday.

The four-week average of jobless claims, regarded as a more reliable guide to future trends, declined by 14,000 to 425,000.

The number of people receiving state unemployment benefits during the week that ended May 21 remained stable at 3.71 million.

Nearly 4 million other people continued to collect payments under a special federal program adopted in the face of the worst economic slump since the Great Depression.

The official U.S. unemployment rate stands at 9 percent.

In a separate report also released Thursday, the Labor Department said the productivity of U.S. firms climbed 1.8 percent in the first quarter, compared with an advance of 2.9 percent in the final three months of 2010.

Unit labor costs, meanwhile, rose at an annualized rate of 0.7 percent in the January-March period after falling 2.8 percent in the fourth quarter of last year.

Real output expanded 3.2 percent in the first quarter of 2011, the Labor Department said.