South Korean authorities are probing the illegal entry of North Korean coal into South Korean ports last year in violation of United Nations sanctions.

Foreign ministry spokesman Noh Kyu-duk said on Tuesday that the authorities are currently investigating the case, adding that the government has been closely cooperating with the international community to faithfully implement the U.N. sanctions on North Korea.   

Earlier in the day, the Voice of America(VOA) reported that the North’s coal was twice shipped to South Korea via Russia last year. 

Citing an annual report submitted by an expert panel under the U.N. sanction committee, the VOA said that North Korean coal shipped to the Russian port of Kholmsk was reloaded and sent to South Korea's Incheon and Pohang ports on October second and October eleventh, respectively.

Under U.N. resolution 2371 adopted by the Security Council in August last year, exports of North Korean minerals, including coal, are banned.