South Korea said it has seized a Panama-flagged vessel days after it impounded a Hong Kong-registered tanker suspected of transferring oil products in worldwide waters.
China denied Friday that it was supplying oil to North Korea, USA Today reported.
A marine official also confirmed the seizure, which he said was done "recently".
The South Korean official said on Friday that the Lightouse Winmore, chartered by a Taiwanese company and carrying oil products from South Korea, had transferred part of its cargo to a North Korean ship on 19 October. They declined to provide details of the probe, and the foreign ministry also said it has yet to receive any formal notification from the related agencies on the inquiry.
The ship had headed towards its purported destination in Taiwan, but on reaching worldwide waters transferred some of its 600 tonne cargo to the Sam Jong 2 and three other North Korean vessels, the South claimed.
However, the vessel not going to its claimed destination transferred the oil to North Korean vessels in worldwide waters in the East China Sea.
The South Korean Foreign Ministry said the vessel departed the port of Yeosu in South Korea on October 19 carrying refined oil that was then transferred to a North Korean ship in global waters.
The KOTI's ties to China also seem clear, the tanker is run by companies operating out of Hong Kong and Dalian, two well-known hubs for North Korean sanctions evasion.
Earlier a foreign ministry official in Seoul had said the ship had been seized briefly by customs authorities who inspected it.
China's Foreign Ministry, responding to a question from Reuters on the blocking, said Beijing always fully and strictly implemented Security Council resolutions.
The U.N. Security Council last month unanimously imposed new sanctions on North Korea for a recent intercontinental ballistic missile test, seeking to limit its access to refined petroleum products and crude oil.
"At the same time, any measures taken by the Security Council must have a basis in conclusive and actual proof".
"We are closely monitoring North Korea's attempts to evade United Nations sanctions".
After Daily Star Online reported China has been going behind the world's back and helping nuke-nut leader Kim Jong-un, it appears Russian Federation has followed suit.
South Korea has seized a second ship as part of what it describes as an ongoing effort to monitor North Korea's attempts to evade United Nations sanctions.