North Korean coal and pig iron worth USD$5.86 million was brought into the South in 2017, the Korea Customs Service (KCS) said on Friday, amid an increasingly deepening domestic scandal regarding the import of sanctioned DPRK-made commodities by South Korean companies last year.

Between April and October last year, the KCS reported in a statement carried by Yonhap, three South Korean groups imported KRW6.6 billion’s worth of the sanctioned goods, representing a potentially major violation of United Nations resolutions.

The companies reportedly transferred the commodities at a Russian port, deliberately mislabeling their country of origin in order to bring them into South Korea.

“The firms appear to have illicitly brought it in expecting big trading margins after prices of North Korean coal had dropped due to the import ban,” KCS deputy commissioner Roh Suk-hwan said, in comments carried by Reuters.

Reports in June by the UN’s Panel of Experts on North Korea revealed that two vessels – the then-Panama-registered Sky Angel and the Sierra Leone-flagged Rich Glory – had unloaded DPRK-produced coal at Incheon and Pohang in October 2017.

Though the panel did not specify the size of the shipments at the time, the South Korean foreign ministry in July said the Sky Angel had shipped 4000 tons of North Korean coal to the South.

The Rich Glory, in turn, was reported to have unloaded 5000 tons of North Korean coal worth around USD$325,000 at Pohang.

Seoul at the time pledged to take action against the two ships and “punish” concerned parties “if necessary.”

Late July saw the KCS admit that “numerous” sanctions-busting ships may have entered ROK ports in 2017, with the Ministry of Foreign Affairs (MOFA) telling NK News at the time that further details of the investigation would be released at an “appropriate time.”

Any imports of North Korean coal by South Korean companies would represent a violation of United Nations Security Council (UNSC) resolution 2371, with resolution 2397 requiring member states to seize vessels suspected of involvement in DPRK-linked smuggling.

A South Korean foreign ministry official on Monday said that Seoul was investigating nine suspected shipments of DPRK-made coal into the South.

Reports in local press have suggested that one entity involved may have been linked to the country’s partially state-owned Korea Electric Power Corporation (KEPCO).

Seoul has so far declined to share further specifics about the companies involved in the case, while insisting that the issue has not caused friction with the U.S.

U.S. State Department spokesperson Heather Nauert on Thursday said that Washington had full faith that the South Korean government would investigate the case thoroughly.

“Look, we trust when they say that they will investigate that they will investigate,” she said. “We closely coordinate with them. They’ve been longstanding allies and partners, and we have a strong relationship with them.”

But despite the ongoing investigation, ship tracking data by NK News’s sister site earlier in the week revealed that South Korean ports were still allowing vessels owned by UN-designated companies to use their facilities.

The Belize-flagged Xin Yang 688, for example, left South Korea’s Pohang Port on Monday before traveling southwards on course for Busan.

The Xin Yang 688’s owner was designated by the UN in March for its role in smuggling North Korean coal in breach of resolutions, via another of its vessels called Asia Bridge 1.