Prices paid by U.S. factories picked up pace in March as the disruption caused by Japan's earthquake began to be felt in the auto industry and fuel prices rose strongly.

Another report on Thursday showed a surprise jump in U.S. jobless claims that raised some questions among investors about the health of the labor market recovery, though economists said the number could be a one-off.

Core U.S. producer prices rose slightly faster than expected in March from February and the increase from a year ago was the largest since August 2009.

The Labor Department said its seasonally adjusted index for prices paid at the farm and factory gate -- excluding volatile food and energy costs -- rose 0.3 percent after gaining 0.2 percent in February.

A combination of concerns about higher inflation in the global economy and the unexpected rise in new claims for unemployment benefits helped push down U.S. stock prices.

Light trucks prices advanced 0.7 percent, the biggest rise since July and accounted for a third of the gain in the core PPI. Passenger vehicle prices increased 0.9 percent, the largest increase since June 2009.

It looks like the disruption to global autos production stemming from the Japanese disaster will hit autos supply and, consequently could lead to some further steep price increases over the next few months, said Paul Ashworth, chief U.S. economist at Capital economics in Toronto.

Suppliers axed their discount for vehicles as they anticipated shutdowns hurting supply, said Brian Bethune, chief U.S. financial economist with IHS Global Insight. They don't want to deplete their inventories too soon, he said.

In the 12 months to March, the core producer price index rose 1.9 percent, the biggest increase since August 2009 and speeding up from February's 1.8 percent rise.

In the 12 months to March, producer prices overall rose 5.8 percent, the largest gain in a year. The monthly gain slowed to 0.7 percent, below the 1.0 percent expected by economists.

Gasoline prices leapt 31.2 percent in the year to March, a reflection of the recovery in the global economy and the concerns about the unrest in the Middle East and North Africa.

Although rising gasoline prices are adding to inflation pressures, the Federal Reserve predicts they will prove transitory. Fed officials have said they would act if necessary to ensure that an inflation psychology does not take root.

Even as price pressures show signs of building, several readings of the U.S. economy have shown weakness recently.

A global poll of economists by Reuters showed the U.S. economy was expected to grow 2.5 percent in the first quarter, a sharp cut from the 3.5 percent seen a month ago. For 2011 as a whole, growth is seen at 2.9 percent, down from the previous forecast of 3.1 percent.

FED WORRIES ABOUT COMMODITY PRICES

The U.S. central bank said in its Beige Book summary of economic conditions on Wednesday that businesses were reporting that higher commodity costs were pushing up prices.

But producers are struggling to pass higher costs to consumers because the labor market remains weak and wage growth is subdued.

A second report from the Labor Department showed initial claims for state unemployment benefits rose 27,000 to a seasonally adjusted 412,000, well above economists' expectations for a fall to 380,000.

Given the underlying downward trend we are inclined to see it as a one-time fluke, though we will be happier if we see a clear reversal next week, said Ian Shepherdson, chief U.S. economist for High Frequency Economics in Valhalla, New York.

Economists have noted an increase in claims often at the end of a quarter.

The four-week moving average of unemployment claims -- a better measure of underlying trends - climbed 5,500 to 395,750.

The rise in claims interrupted a downward trend that had kept them below the 400,000 threshold for four weeks.

That level is normally associated with steady job growth. Despite last week's rise, the four-week average held below the 400,000 mark for a seventh straight week.

Energy prices, which rose 2.6 percent, accounted for nearly 90 percent of the increase in wholesale prices last month. Energy prices rose 3.3 percent in February.

Gasoline prices rose 5.7 percent after increasing 3.7 percent in February. Food prices fell 0.2 percent, the first decline since August.

(Reporting by Lucia Mutikani; Editing by Neil Stempleman)

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