South Korean authorities seized a Hong Kong tanker after it was found to have secretly transferred 600 tons of refined petroleum to a North Korean vessel in international waters in October, in a brazen breach of UN sanctions.

Acting on intelligence provided by the US - including surveillance photos of an exchange taken by satellite - South Korean customs officials boarded the vessel, the Lighthouse Winmore, when it entered Yeosu Port on November 24, Yonhap news reported.

The investigation has so far determined that the ship was chartered by a Taiwanese company, Billions Bunker Group, and had initially docked in Yeosu Port on October 11 to take on a cargo of Japanese refined petroleum before going on to its final declared destination of Taiwan four days later.

After leaving port, however, the Hong Kong ship met up with the Sam Jong 2, a 2,507-ton North Korean tanker, and three other unnamed ships in international waters in the East China Sea.

Under United Nations Security Council resolution 2375, which was adopted in September, companies or organisations of member states are not permitted to carry out the ship-to-ship transfer of any goods that are bound for North Korea.