September's producer price index rose 6.3% on an annual basis, the largest 12-month increase since climbing 6.1% in December 2022, according to the Bureau of Labor Statistics.

The producer price index measures the average change over time in the selling prices received by domestic producers for their goods, services, and construction. It's considered a measure of underlying inflationary pressures, and September's figures came in much higher than economists had forecasted, CNBC reported. 

The index rose 1.3% over August, according to the BLS data released on Thursday. Both the monthly and annual increase exceeded forecasts of economists polled by Dow Jones, who expected an increase of 0.6% for the month and 5.5% for the year. 

Energy was a primary driver of the increase as the Middle East conflict continues to restrict the oil supply and the war in Ukraine continues to reduce refined petroleum products on the global market. 

Excluding food, energy and trade, the PPI rose 0.5% in September and 5% on an annual basis.