Voice of America (VOA) revealed in a report Thursday that two ships, one from Sierra Leone and another from Panama, were involved with the illegal shipment of North Korean coal to South Korea and have recently re-entered the South’s ports multiple times in violation of international law.

South Korea has reportedly cracked down in response to this.

Rich Glory, registered to Sierra Leone, reportedly entered the South Korean port of Pohang, on October 11, carrying coal from North Korea. VOA also reported that Sky Angel, registered to Panama, shipped North Korean coal from Russia’s Kholmsk to South Korea’s Incheon on Oct. 2, 2017, and that the ship entered the port of Ulsan, near Busan, on June 14.

In August 2017, the United Nations Security Council adopted U.N. Resolution 2371, which states that the export of North Korean minerals, including coal, is banned.

“Unanimously adopting resolution 2371 (2017) under Article 41, Chapter VII of the United Nations Charter, the 15-nation Council decided that the Democratic People’s Republic of Korea shall not supply, sell or transfer coal, iron, iron ore, seafood, lead and lead ore to other countries,” the resolution states.

According to South Korea’s Yonhap News, Rich Glory was again detected in the port of Busan, in South Korea, at 11:58 a.m. on July 4.

The publication further noted that “Rich Glory has visited South Korean ports at least 16 times over the past nine months without any restraints from the Seoul government and is currently navigating in Japanese waters.”

Following the report from VOA, South Korea’s ministry spokesman Noh Kyu-duk reportedly said in a press briefing, “The relevant authorities are currently investigating the case and, if necessary, punishment will be imposed. Those incidents will serve as an opportunity to realize the significance of the U.N. Security Council sanctions.”

He reiterated that South Korea’s position against conducting trade and commerce with North Korea will remain in place until the South is convinced that the North has complied with its vows to denuclearize completely.

“The government has been making diplomatic efforts, together with the international community, to ensure that the U.N. Security Council sanctions are faithfully implemented,” Noh reportedly said.

Yonhap News noted that VOA has suggested China, a strong North Korean ally, may be responsible for coordinating the illegal shipment of North Korean coal to South Korea through Russia last year.

China also voted for U.N. Resolution 2371, which passed unanimously. Upon signing, China’s import of North Korean coal was reportedly reduced by 60 percent compared with that same period of time the year before.

Adelle Nazarian is a politics and national security reporter for Breitbart News. Follow her on Facebook and Twitter.