South Korea's grain imports dropped nearly 6 percent on-year in the first half due to weaker international prices and decreased domestic demand, government data showed Friday.

Imports of corn, wheat, rice, barley and oats reached US$1.86 billion in the January-June period, down 6.1 percent from $1.98 billion tallied the year before, according to the data by the Korea Customs Service (KCS).

In volume terms, the total imports hit 7.22 million tons, down 0.8 percent from 7.27 million tons in the first half of 2014.

The decrease came as most grain prices have fallen on the international market due to increased supplies.

The five key grains account for 99.8 percent of all cereal imported by Asia's fourth-largest economy, with corn alone making up 70.8 percent of the total. Wheat and rice accounted for 26 percent and 2.4 percent of all grain imports, respectively.

The report showed corn imports sank 12.5 percent on-year to $1.14 billion in the first half.

Numbers for wheat, rice and barely all fell vis-a-vis the year before, while imports of oats rose in both monetary and volume terms.

The customs service said the United States was the largest exporter of corn and wheat, with China being the No. 1 supplier of rice. Australia shipped the most barley, with Canada being the main exporter of oats.