Small businesses in the United States stepped up hiring last month with more than half adding jobs or trying to fill open positions, suggesting an improving labor market as others surveyed said they planned to create jobs.Overall, 14 percent of small firms added an average of 2.7 workers per firm last month, while 12 percent said they planned to add jobs, according to a survey by the National Federation of Small Business released on Thursday.

The survey found 29 percent of small businesses said they had trouble finding qualified workers to fill open positions, the highest level since April 2006. That was up from 27 percent last month.

"This is a strong indication that the unemployment rate will decline further, even if the report of employment growth is sub-par. The supply of available qualified labor is not large enough relative to even weak labor demand to keep the unemployment rate higher," NFIB's chief economist William Dunkelberg said in a statement.

Of the businesses surveyed, 12 percent said they had cut an average of three jobs each last month.

NFIB's report comes ahead of the more comprehensive employment report that the U.S. Department of Labor will release on Friday.

Analysts polled by Reuters expect the federal data to show U.S. employers added 225,000 jobs in May, up from 223,000 in April. The unemployment rate is expected to remain unchanged at 5.4 percent.

Separate U.S. data earlier on Thursday showed the rate of new applications for unemployment insurance fell last week and continued claims dropped to their lowest level since 2000.

The NFIB survey collected responses from 616 small businesses.

"While small business historically leads economic recoveries, this time they are slowly catching up to their larger counterparts," Dunkelberg added.