A closely watched consumer survey from the University of Michigan has fallen to its lowest level in more than a year.
The index on US consumer sentiment fell to 66.6 in early September from 68.9 in August.
Meanwhile, official figures show that US consumer prices increased by slightly more than expected in August as food prices rebounded and energy costs remained high.
The Labor Department said its seasonally adjusted Consumer Price Index rose 0.3% after rising 0.3% in July. Analysts had expected a 0.2% increase.
Core prices, which exclude more volatile food and energy prices, were flat compared with July.
In the 12 months to August, the CPI rose 1.1%, compared with an annual increase of 1.2% in July. The annual rise was in line with market expectations.
