SEOUL, South Korea (AP) — South Korea says a total of 35,000 tons of North Korean coal and pig iron worth $5.8 million illegally entered its ports last year, in possible violations of UN sanctions. The Korea Customs Service said Friday it is seeking prosecutions of three local companies and their executives for smuggling or falsely saying North Korean mineral resources came from Russia. Officials say they are also looking into whether any of the 14 vessels that transported North Korean coal violated sanctions banning such shipments.

The announcement followed a 10-month investigation.

The United Nations Security Council first imposed sanctions on North Korea after its first nuclear test in 2006. A recent report to the Security Council found Pyongyang has been violating U.N. sanctions with clandestine shipments of coal, oil and military equipment.