Specialized railcars associated with North Korea's past movement of radioactive material have reportedly been spotted at its Yongbyon Nuclear Scientific Research Center.

The observation was revealed on Tuesday by Victor Cha, Korea Chair of the Center for Strategic and International Studies(CSIS), and the think tank's senior fellow Joseph Bermudez Jr. 

In their assessment on the Beyond Parallel Website, the researchers pointed to satellite imagery they obtained the previous day that shows three railcars on a track to the west of the radiochemistry laboratory at the nuclear facility, which also serves the North's uranium enrichment plant.

It is the first time the railcars have been spotted at the location since November 14, 2019.

Noting the relatively small size and number of casks on the railcars, Cha and Bermudez suggested there may be an outbound shipment of small quantities of irradiated liquid or solid waste, disassembled but contaminated equipment or fissile material to facilities outside the Yongbyon area.

Although less likely, the researchers also suggested there may be an inbound shipment of radioactive material from an outside facility.