SEOUL (Yonhap) - South Korea's crude oil imports from Iran have more than doubled this year following the lifting of sanctions in January as major refiners have ramped up purchases of cheaper oil offered by the Middle Eastern nation, the state-run oil company said Sunday.

A total of 30 million barrels of Iranian crude and condensate were shipped to South Korea in the first four months of this year, up 113.5 percent from a year earlier, the Korea National Oil Corporation (KNOC) said.

The annual import of Iranian crude was at 87.2 million barrels in 2011, but it dropped to 56.1 million barrels in the next year in the wake of sanctions imposed for its nuclear program and further dipped to 44.9 million barrels in 2014, the KNOC said.

In the run-up to Iran's landmark nuclear deal last year South Korean refiners sought to expand imports of Iranian oil, which is $5-6 cheaper a barrel than Qatar crude that holds a dominant market position.

SK Innovation Co., South Korea's leading refiner, and No. 4 Hyundai Oil Bank Co. have expanded purchases of Iranian oil, followed by Hanwha Total Petrochemical Co., a chemical unit under Hanwha Group, in April.

In contrast, neither GS Caltex Corp., the nation's second-largest refiner half owned by U.S. oil giant Chevron, nor its smaller rival S-Oil Corp., a local unit of the world's largest crude exporter Saudi Aramco, import Iranian oil.

"Imports of Iranian oil will increase once remaining hurdles such as U.S. dollar settlement are lifted when trading with Iran," an official at one of the refiners said.