South Korea's producer prices declined for the 12th straight month in September on falls in prices of oil and agricultural products and the local currency's gain against the U.S. dollar, the central bank said Thursday.

The producer price index, a barometer of future consumer inflation, slid 1.8 percent in September from a year earlier, compared with a 1.3 percent on-year decline in August, according to the Bank of Korea (BOK).

The September data marked the sharpest on-year fall since a 2.6 percent on-year decline in May. On an annual basis, the producer prices have fallen every month since October 2012, when such prices fell 0.5 percent on-year.

Prices of Dubai crude, South Korea's benchmark, fell 2.9 percent in September from a year ago, compared with a 1.4 percent on-year fall in August. The Korean won appreciated 3.44 percent to the greenback in September compared with a year earlier.

A BOK official said that prices of fruits and vegetables sharply declined compared with a year earlier, as there was no damage from typhoons this year.

Compared with a month earlier, the producer prices inched down 0.1 percent after rising 0.3 percent in August.

The data came as the BOK froze the key interest rate at 2.5 percent for the fifth straight month in October.

Korea's consumer prices remained subdued, running below the central bank's 2.5-3.5 percent inflation target band for 2013-2015.

Korea's consumer inflation grew 0.8 percent in September from a year earlier, the slowest pace in 14 years, due to falls in prices of farm products. (Yonhap News)