In a joint statement from the foreign and trade ministries and the customs service, the South Korean government said it is "checking additional information concerning the loading cases reported by the Guardian" and "if the verification establishes that our laws and regulations have been violated, it plans to act in accordance with the law."
The Guardian's analysis of port records and ship-tracking data found that seven tankers loaded the fuel at several South Korean ports. Three of the tankers are under UK and EU sanctions. One sanctioned vessel took on about 26,000 tonnes through a ship-to-ship transfer at an anchorage off the southern port of Yeosu.
Isaac Levi, an analyst at the Centre for Research on Energy and Clean Air (CREA), a Finnish thinktank, said the trade "undermines the sanctions regime and South Korea's support for Ukraine."
Russia's capacity to refine oil has been severely disrupted by Ukrainian drone strikes. According to the International Energy Agency, Russian refinery throughput fell in June to its lowest level in more than 20 years, and diesel output is down nearly 30% on last year.
The South Korean statement said the refined petroleum products involved are not covered by South Korea's export controls on Russia, which apply mainly to industrial machinery, electronics and vehicles. It noted that "the loading of refined petroleum products at our ports does not constitute a violation of our domestic law."
The government said whether fuel of South Korean origin, such as diesel, had been exported "has not been confirmed" and added that no diesel, aviation fuel or motor petrol had been "exported" from South Korea to Russia through customs clearance. It is unclear who owned or sold the fuel, as South Korean port records do not show this publicly.
The government also cautioned that the "mere fact that a vessel did not proceed directly to the final destination country stated on its declaration and instead moved to another country makes it difficult to conclude that there is a suspicion of false declaration of destination." It said it would examine the tankers' actual routes, any divergence from their declared destinations and the reasons for them. The three sanctioned tankers had told South Korean authorities they were bound for Japan or Singapore before sailing to Vladivostok.