One of North Korea’s largest active service bulk carriers delivered coal to the Chinese port of Longkou and returned with white-bagged cargo, satellite imagery and ship tracking data suggest, in the latest sign North Korea could be engaged in a sort of barter system with China.

In early March, satellite imagery from PlanetLabs showed a 175-180 meter-long vessel docked directly adjacent to a conveyor system, itself connected directly to a 285,000 square foot coal depot. The ship undocked sometime between March 7 and March 10, and on March 13, ship tracking data shows the Rina (IMO 9133290), a 28,700-ton bulk carrier