A sanctioned North Korean oil tanker has been photographed in the process of conducting suspected illegal ship-to-ship (STS) transfers at sea in relay fashion with two unidentified ships, the Japanese Ministry of Foreign Affairs (MOFA) said in a statement Tuesday.

It is the third such instance the North Korean-flagged An San 1 has been observed conducting STS transfers by Japanese Maritime Self-Defense Forces since the ship was designated in March 2018 by the UN Security Council committee in charge of DPRK sanctions.

STS transfers at sea are known as one way North Korea is circumventing current sanctions restricting the flow