U.S. business inventories unexpectedly rose 0.3 percent in September as unsold stocks of autos accumulated at the fastest clip since February, a government report showed on Monday.

Analysts polled by Reuters had been expecting inventories to remain unchanged.

Motor vehicle and parts inventories rose 1.5 percent, the sharpest increase since a 2.1 percent rise in February, the Commerce Department (search) said. Retail inventories excluding cars rose 0.8 percent, the steepest climb since May 2000.

It was the biggest rise in overall inventories since a matching 0.3 percent gain in March.

At the same time, total business sales climbed 0.6 percent in September as building materials, general merchandise, and home furnishings sales posted modest gains. Auto sales slid 2.2 percent, Commerce said.

The drop in overall inventories kept the stock-to-sales ratio — a measure of how long it would take to deplete stocks at the current sales pace — at a record low 1.36 percent for the third month in a row.