U.S. producer prices unexpectedly fell in September and the increase in the annual rate was the smallest in nearly four years, pointing to a benign inflation environment.

The Labor Department said on Tuesday its seasonally adjusted producer price index dipped 0.1 percent last month, the first decline since April, after advancing 0.3 percent in August.

A Reuters survey of economists had forecast prices received by the nation's farms, factories and refineries would rise 0.2 percent in September.

In the 12 months through September, wholesale prices rose 0.3 percent, the smallest gain since 2009. That compared to a 1.4 percent increase in August.

Wholesale prices excluding volatile food and energy costs nudged up 0.1 percent after being flat in August. In the 12 months through September, the so-called core PPI increased 1.2 percent after rising 1.1 percent in August.

The tame wholesale inflation reading, coming on the heels of weak home sales and manufacturing production, as well as sluggish hiring, could offer the Federal Reserve ammunition to stick with monthly bond purchases aimed at stimulating the economy through low interest rates.

Officials from the central bank meet on Tuesday and Wednesday to assess the economy and deliberate on monetary policy. They are expected to keep the monthly $85 billion bond purchasing program in place until at least next March, according to a Reuters poll.

A drop in wholesale food prices offset a rise in the cost of energy, depressing overall producer prices. Food prices fell 1.0 percent as the cost of processed poultry recorded its biggest decline since February 2011.

Wholesale gasoline prices fell 0.1 percent.

Core PPI was lifted by a 0.9 percent increase in the price of light motor trucks, which was the biggest gain since July 2012, while cosmetics recorded their biggest rise since June 2010.