US wholesale prices jumped 0.4 percent in May due to a surge in fuel costs, but core prices fell for the first time since October, the Labor Department reported Wednesday.
The overall rise in the producer price index (PPI) was unsurprising, after a surge in crude oil prices.
But the fall in the core index -- which strips out volatile fuel and food prices -- was another sign of weak inflation, which has been a concern of the Federal Reserve.
That put the year-on-year gain in core PPI at just 0.8 percent.
The Federal Reserve, which finishes a two-day meeting on monetary policy Wednesday afternoon, has kept interest rates at an ultra-low level to boost consumer inflation up towards a target of two percent.
The new PPI data could support an expected decision to further delay planned interest rate increases until they see an upturn in prices.