The Lighthouse Winmore is believed to have "secretly transferred" about 600 tons of refined petroleum products to the North Korean ship, the Sam Jong 2, in international waters in the East China Sea on Oct. 19, according to Bloomberg and the Associated Press.

The Hong Kong vessel had previously visited Yeosu port on Oct. 11 to load up on Japanese oil products and departed the port while claiming its destination was Taiwan. Instead, it transferred the oil to the Sam Jong 2 and three other non-North Korean vessels in international waters

The vessel was chartered by Taiwanese company Billions Bunker Group, which is incorporated in the Marshall Islands. According to Bloomberg, Taiwanese investigators are looking into whether any Taiwanese nationals have ties to the ship that was seized on Friday, Taiwan's Maritime and Port Bureau says in statement on its website.