The South Korean government says it is investigating South Korean companies possibly responsible for illegally importing North Korean coal.

The Korea Customs Service(KCS) is focusing on the question of whether local importers knowingly brought in North Korean coal. 

The government is considering possible punitive measures against two foreign vessels allegedly used to bring in the coal. 

A Foreign Ministry official says Washington has expressed no concerns over the issue, noting Seoul is closely cooperating on the faithful implementation of the UN Security Council’s sanctions on the North. 

According to the recently revealed UNSC documents, the North shipped its coal from Russia to a third country via South Korean ports twice, late last year.