The American private sector added less jobs than forecast in May, signaling that the labor market needs more time to recover, a leading industry report revealed Thursday.

The U.S. private sector added 133,000 jobs in May on a seasonally adjusted basis, less than economists' average estimate of 150,000.Estimated gains for April were also revised lower to 113,000, according to the National Employment Report released by Automatic Data Processing, Inc. (ADP).

Small and medium businesses accounted for the majority of the employment gains this month, adding 124,000 jobs in total. Large businesses added only 9,000 jobs during the period.

Employment in the service sector rose by 132,000 in May after increasing 123,000 a month earlier. Jobs in the goods-producing sector increased bt 1,000, according to the report.

Economists say that the current pace of job growth is not very impressive and is consistent with an economy that is growing modestly.

U.S. economic growth slowed to an annualized pace of 1.9 percent in the first quarter of the year, down from the initial estimate of 2.2 percent, according to revised figures released Thursday by the Commerce Department.

In the beginning of 2012, American businesses added an average of over 200,000 net jobs per month. But job growth has declined recently, sparking fresh worries over labor market recovery.