The U.S. manufacturing sector expanded in May, but at a slower rate than in April, according to the Institute for Supply Management's manufacturing purchasing managers' index released today.

In May, the index slipped to a level of 59.7 from 60.4 in April. However, a reading above 50 indicates manufacturing activity is generally expanding. May's reading reflects the 10th month of expansion in the manufacturing sector.

The employment portion of the manufacturing index rose to 59.8 in May from 58.5 in May.