The customs agency says North Korean coal and pig iron worth billions of won were smuggled into South Korea last year, in a potential violation of sanctions against Pyongyang. 

The Korea Customs Service(KCS) on Friday held a news conference and unveiled the results of its probe on the illegal entry of North Korean coal into South Korea. 

According to the agency, three South Korean firms smuggled into the country 35-thousand tons of North Korean coal and pig iron, valued at six-point-six billion won, between April and October of last year. 

The KCS said the three companies illegally brought in the coal and pig iron after fabricating the certificate of origin to make it seem the resources were Russian. 

Under UN Security Council Resolution 2371, adopted just last year, North Korea is banned from exporting coal, iron ore and other mineral resources and countries are obligated to capture and inspect a vessel suspected of illegal activities involving the regime.