By Kang Seung-woo

Korea's imports of Iranian oil nosedived in December, hitting a 14-month low, as the U.S. government stepped up its imposition of sanctions to weaken Tehran economically and derail its suspected pursuit of nuclear weapons.

According to data from the Korea Customs Service (KCS), Korean imports of Iranian crude were measured at 639,000 tons in December, a 46.5 percent decline from 1.19 million tons brought in the preceding month. The volume of Iranian oil purchased last month also represented nearly a 17 percent annual drop and marked the lowest level since October 2010, when Korea imported 528,000 tons.

Iran is the second-largest oil producer in the Organization of Petroleum Exporting Countries (OPEC). One of its major markets has been Korea, the world's fifth-largest crude importer, which bought 12.42 million tons of crude from the Middle Eastern country last year, accounting for around 9.8 percent of its total oil imports, according to the Korea National Oil Corp. (KNOC). Supplies from Iran accounted for 10 to 12 percent of total crude imports from August to November last year, but only 5.9 percent in December.

Observers attribute the drop to local refiners' quick reaction to reduce their dependence ahead of the government's possible measures to halt oil imports from the country.

"There has been no guideline from the government to companies to slash oil imports from Iran. As the government announced new economic sanctions against Iran last month and the United States took a tougher stance on the country, local refiners may have taken preventative measures," said a government official.

Washington is pressing Seoul to reduce its oil imports from Iran as part of its sanctions over Tehran's alleged nuclear weapons program.

U.S. President Barack Obama last month signed a bill imposing tough penalties on financial institutions dealing with Iran's central bank. Robert Einhorn, the State Department's special adviser for nonproliferation and arms control, Tuesday urged Korea to help the United States to increase pressure on the Iranian government during his three-day visit to Seoul.

However, industry watchers say that the import contraction may have stemmed from a one-off factor which has to do with the amount of inventory.

Among the nation's four oil refiners, SK Innovation and Hyundai Oilbank import about 10 and 20 percent of their crude oil requirements respectively from Iran.