U.S. wholesalers increased their stockpiles at a slower pace in May as sales fell by the most in three years.

Wholesale inventories increased 0.3 percent to $484.1 billion, in line with economists' forecast, the Commerce Department said Wednesday. April's reading was revised slightly lower to show a gain of 0.5 percent.

Inventories are a key component of the government's calculation of gross domestic product. The data on wholesale inventories appeared to have further confirmed many economists' view that the economic growth in the U.S. slowed in the second quarter.

We have lowered our U.S. Q2 2012 real GDP forecast to an annualized 1.5 percent from 2.5 percent, Dean Maki, an economist at Barclays Capital, wrote in a note to clients this morning.

Stockpiles of nondurable goods fell 0.2 percent from April, dragged down by a 5.1 percent decline in farm products and a 3.6 percent drop in petroleum stockpiles.

Inventories of durable goods, such as machinery, automobiles and furniture, increased 0.6 percent in May.

Sales at wholesalers fell 0.8 percent in May, held back by a 4.7 percent decline in petroleum sales. That was the sharpest drop for both reading since March 2009.

Enough goods were kept on hand by the wholesalers to last 1.18 months at the current sales pace in May, the highest reading since July 2011.