The number of Americans filing for jobless aid rose to an eight-month high last week and productivity growth slowed in the first quarter, clouding the outlook for an economy that is struggling to gain speed.

While the surprise jump in initial claims for unemployment benefits was attributed to factors ranging from spring break layoffs to the introduction of an emergency benefits program, economists said it corroborated reports this week indicating a loss of momentum in job creation.

New claims for state jobless benefits rose 43,000 to a seasonally adjusted 474,000, the highest since mid-August, the Labor Department said on Thursday. Economists had expected claims to fall to 410,000.

A second report from the department showed nonfarm productivity increased at a 1.6 percent annual rate, braking from a 2.9 percent pace in the fourth quarter. The growth pace was above economists' expectations for 1 percent.

We do not think that the entire rise in claims over the last month can be explained by special factors alone, said Harm Bandholz, chief U.S. economist at UniCredit Research in New York. It seems instead as if the improvement in the labor market slowed a bit.

Reports this week showed weaker employment growth in the manufacturing and services sectors in April. Data from payrolls processing firm ADP Employer Services also showed a step back in private hiring last month.

The claims data falls outside the survey period for the government's closely watched employment report for April, which will be released on Friday. Nonfarm payrolls increased 186,000 last month, according to a Reuters survey, after rising by 216,000 in March -- which was the most in 10 months.

But the odds are high for an even lower number. The anticipated slowdown in hiring is mostly blamed on high food and gasoline prices, which clipped economic growth in the first quarter. Still, the unemployment rate is expected to have held at a two-year low of 8.8 percent.

U.S. stocks opened lower on the claims report, while government debt prices rose for a sixth straight session. The dollar gained against the euro after the European Central Bank offered few clues on the timing of the future interest rate increases.

SPECIAL FACTORS TO BLAME

Other reports on Thursday showed a late Easter boosted sales of clothing and other holiday-related items in April, but retailers warned rising costs and a weak labor market would dampen purchases over the next several months.

While special factors were blamed for the rise in claims last week, even the four-week moving average of unemployment claims -- a better measure of underlying trends -- increased 22,250 to 431,250, the highest since November.

A Labor Department official attributed the surprise surge in claims last week to spring break layoffs in New York, which added 25,000, and the start of an emergency benefits program in Oregon, which brought in new claimants, including some already on the regular programs.

There were also additional claims from the auto sector, related to plant shutdowns because of parts shortages in the wake of the devastating earthquake and tsunami in Japan.

Deadly tornadoes that struck parts of the country could also have accounted for small number of claims, the labor official said.

The New York spring break fell outside the dates the department uses for seasonal adjustments to account for the holiday nationwide.

Even though claims trended higher the previous week, some economists cautioned against reading too much into last week's surge and expected claims to come down in the weeks ahead.

We are hesitant to take too strong of a signal from the recent increase in claims data and will look to upcoming reports before suggesting that the upturn in claims is a sign that the labor market has lost momentum, said Michael Gapen, a senior economist at Barclays Capital in New York.

But the productivity report offered some hope for the labor market recovery.

While the step back in productivity was flagged by a sharp pull back in economic growth in the first quarter, it also suggested businesses have probably little room to continue cost cutting strategies and may soon need to step up hiring.

Productivity -- which measures hourly output per worker -- rose rapidly in the past two years, peaking at an 8.9 percent rate in the second quarter of 2009. Businesses are estimated to be sitting on $2 trillion in cash.

The economy grew at a 1.8 percent pace in the first three months of this year after expanding at a 3.1 percent rate in the fourth quarter.

The productivity report showed a rebound in unit labor costs, which rose at a 1 percent rate in the first quarter after declining 1 percent in the prior period, but still remaining tame.

High food and energy prices have stoked inflation fears, but Federal Reserve officials see limited scope for a broad pick up in price pressures.

(Editing by Chizu Nomiyama)

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