U.S. nonfarm productivity fell less sharply than previously thought in the first quarter, but labor-related costs still surged as companies employed more workers to boost output.

The Labor Department said on Tuesday productivity, whichmeasures hourly output per worker, contracted at an annualized rate of 0.6 percent, instead of the 1.0 percent pace reported last month.

The revision, which reflected modestly higher output than previously estimated, was in line with economists' expectations.

Productivity fell at a 1.7 percent rate in the fourth quarter. The government last month raised its first-quarter economic growth estimate to a 0.8 percent rate from the 0.5 percent pace reported in April.

U.S. financial markets were little moved by the report.

Productivity, which has only increased in two of the last six quarters, rose at a 0.7 percent rate compared to the first quarter of 2015.

The weakness in productivity partially explains the divergence between the economy's anemic performance at the start of the year and a fairly strong labor market, marked by average monthly job gains of 196,000 in the first quarter.

Some economists have attributed the weak productivity to thechanging industry mix, which has seen a shift from manufacturingand energy toward the production of services. Productivity increased at an annual rate of less than 1.0percent in each of the last five years, suggesting the economy's potential rate of growth has declined.

That would imply the spare capacity in the economy is being squeezed out more quickly than thought and that inflation pressures may take hold a bit faster than had been anticipated.

"The slower pace of productivity gains in recent years suggests the economy's potential rate of growth has fallen," said Sam Bullard, a senior economist at Wells Fargo in Charlotte, North Carolina.

"Thus, even with economic growth of around only 2 percent for the remainder of the year, inflation is likely to rise if corporations aim to maintain margins."

Unit labor costs, the price of labor per single unit of output, increased at a revised 4.5 percent pace in the first quarter. They were previously reported to have advanced at a 4.1 percent rate.

Fourth-quarter unit labor costs were revised to show a 5.4 percent rate of increase, the fastest rate since the fourth quarter of 2014, instead of 2.7 percent.

Despite the upward revision, the trend in labor cost increases remains moderate. Unit labor costs increased at a 3.0 percent rate compared to the first quarter of 2015.

Hourly compensation per hour increased at an upwardly revised 3.9 percent rate in the first quarter instead of the previously reported 3.0 percent pace. 

By Lucia Mutikani - Reuters (Editing by Andrea Ricci)