U.S. hiring plunged in May to its lowest level in more than 5 years, a sign that employers turned cautious after the economy barely expanded in the first three months of the year.

The Labor Department says employers added just 38,000 jobs last month, the fewest since September 2010. Yet the unemployment tumbled to 4.7 percent from 5 percent. That is the lowest rate since November 2007.

The rate fell for a problematic reason: Nearly a half-million unemployed Americans stopped looking for work, and were no longer officially counted as unemployed.

The disappointing figures will likely raise doubts that the Federal Reserve will boost the short-term interest rate it controls at its upcoming meetings in June and July. Many analysts had expected an increase by July.