Authorities were not immediately available for confirmation of the report. She didn't elaborate on the specific activities crew members were suspected of. He could not clarify whether they belonged to mainland China or Hong Kong.
"The vessel is under inspection for alleged ties with North Korea", a government official said, according to Yonhap.
The Lighthouse Winmore visited Yeosu on October 11 and loaded some 14,000 tonnes of Japanese refined oil before heading towards its purported destination in Taiwan.
The authorities said most of the ship's crew are Chinese and Myanmarese.
Results of the investigation will be reported to the UN Security Council's sanctions committee, foreign ministry officials said.
Speaking on condition of anonymity, one western security source said: "Russian vessels have made ship-to-ship transfers of petrochemicals to North Korean vessels on several occasions this year in breach of sanctions".
Russian Federation denied the reports on Saturday, saying via its foreign ministry that it "fully observes fully the sanctions regime" against North Korea.
Taiwan's transport ministry said it is investigating whether any Taiwanese entities were involved. There was nobody Friday at the address given for the firm on Hong Kong's companies registry.
The South Korean Foreign Ministry told CNN Sunday that authorities have launched an investigation into a ship it has seized, but it would not give further details "due to the sensitivity of the issue", about whether that vessel was suspected of transferring oil to North Korea in violation of global sanctions on the hermit kingdom.
The tanker has a capacity of 5,100 tonnes and is suspected to have carried out a ship-to-ship oil transfer to a North Korean vessel. Only four of the ships on the US list, the ones belonging to North Korea including Sam Jong 2 and Rye Song Gang 1, were blacklisted at a session held on Thursday, as AFP reported.
Last week the UN Security Council unanimously adopted new sanctions on North Korea in response to Pyongyang's November 29 ballistic missile test, seeking to further strangle its energy supplies and tighten restrictions on smuggling and the use of North Korean workers overseas.