US producer prices rose a steeper-than-expected 0.5 percent last month as food prices posted their biggest gain in more than 2-1/2 years, but prices outside of food and energy rose just 0.2 percent, the government said on Tuesday.

The rise in the producer price index -- a measure of prices received by farms, factories and refineries -- outstripped expectations on Wall Street for just a 0.3 percent gain, but the increase in the core index matched forecasts.