Chinese ships have congregated in North Korean waters unusually far from the country’s main port of Nampho in recent weeks, ship-tracking data and satellite imagery show, while several ship-to-ship transfers appear to have taken place in the area.

The activity suggests vessels are assembling outside established staging areas to avoid detection, as ship-to-ship transfers are a key part of the DPRK’s sanctions evasion strategy.

According to maritime tracking database MarineTraffic, at least three Chinese-flagged ships — the Shan He, Jin Ye 18 and Ciyan 178 — anchored close to one another roughly 35 nautical miles (56 kilometers) from Nampho