The number of planned layoffs in U.S. companies climbed to a 16-month high in July, according to consulting firm Challenger, Gray & Christmas, Inc.

Corporations unveiled 66,414 planned job cuts last month, up a sharp 60.3 percent from 41,432 in June. On a year-over-year basis, job cuts spiked by 59.4 percent from the 41,676 job cuts announced in July 2010.

The July figure was the highest monthly number of job eliminations since March 2010.

"What may be most worrisome about the July surge is that the heaviest layoffs occurred in industries that, until now, have enjoyed relatively low job-cut levels," said John A. Challenger, chief executive officer of Challenger, Gray & Christmas, in a statement.

Indeed, layoffs from firms in the pharmaceutical and retail industries dominated the picture last month, overtaking the government.

Merck & Co., Borders, Cisco Systems, Lockheed Martin and Boston Scientific accounted for 57 percent of all July job cuts, according to Challenger.

"A casual observer certainly might conclude that the wheels just fell off the recovery wagon," said Challenger.

However, on a year-to-date basis, 2011 is actually better than 2010 in terms of layoffs.

Through the first seven months of 2011 employers have announced 312,220 cuts, a decline of 8 percent from the comparable period in 2010.