Four North Korean vessels, three of which have been linked to illicit sanctions-breaking networks, were allowed to enter a Chinese port which handles coal between Wednesday evening and Thursday morning, analysis of positional information from ship tracking site Marine Traffic shows.

The four vessels are all owned by Pyongyang-based companies and have been waiting near the port for over two weeks.

Satellite imagery of the facility – located near Tangshan in China’s northeast – shows that the area of the port where three of the vessels are docked mainly handles coal, while the fourth is located at a nearby pier that