According to preliminary data from the Korea Customs Service, South Korea imported 1.8 million tons of crude oil, 13.2 million barrels, from Iran in January, up 108.8 percent from a year ago, Reuters reported.

Seoul imported a total of 12.4 million tons of crude last month. In January 2016, South Korean refineries shipped in 10.9 million tons, the data showed.

Iran had been a major exporter of crude to South Korea, but anti-Tehran sanctions had reduced bilateral trade between the two nations.

This changed after Iran and the Group 5+1 (Russia, China, the US, Britain, France and Germany) reached a nuclear deal in July 2015 and started implementing it on January 16.

The comprehensive nuclear deal, known as the Joint Comprehensive Plan of Action (JCPOA), terminated all nuclear-related sanctions imposed on Iran.