A cargo ship suspected of carrying coal has been spotted at a North Korean port, a US broadcaster said Wednesday, raising the possibility of a violation of global sanctions on Pyongyang.

The 110-meter-long ship was spotted docked at the North's western port of Nampo along with plenty of black materials nearby in a satellite photo taken Tuesday by the U.S. Earth imaging company Planet Labs, according to Voice of America (VOA).

The ship was first seen at the port in a satellite photo taken Saturday when it was docked 30 meters behind what was spotted in the Tuesday photo. The movement might be aimed at loading what appears to be coal, the VOA said.

At least four such ships have been seen spotted at Nampo for three to four days this month, it added, raising suspicions that they could have been used to carry coal.

North Korea is banned from exporting coal, iron ore and other mineral resources under Resolution 2371, passed in Aug. 2017.

UN sanctions call for a country to capture and look into a vessel suspected of engaging in prohibited activities with North Korea.

Coal is a key export item for the impoverished country, and Nampo is known as a major port for coal shipment.

Suspicions are mounting that North Korea is evading such export restrictions through diverse ways. In March, the US Department of Treasury said that North Korea continues to evade global sanctions on its exports of coal and refined oil through illicit ship-to-ship transfers. (Yonhap)