The Lighthouse Winmore, which was chartered by a Taiwanese company and carrying around 600 tonnes of oil products from South Korea's Yeosu port, transferred part of its cargo to a North Korean vessel on October 19, the official said.
A Reuters report on Friday also cited two unnamed European intelligence agencies saying that tankers operating out of the Russian Far East were also transferring oil to North Korea at sea.
The crew of a Hong Kong-registered ship have been detained for questioning in South Korea since their tanker was impounded in November for transferring oil to a North Korean vessel and breaching United Nations sanctions, customs officials said Saturday.
"The actions taken will be reported to the UN Security Council sanctions committee on North Korea in the future".
The authorities said most of the ship's crew are Chinese and Myanmarese. "As for the KOTI, an investigation is underway", a foreign ministry spokeswoman told CNN by telephone.
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 worldwide waters in the East China Sea.
Russian Federation denies North Korea sanctions breach claims
The Sam Jong 2 was one of four ships barred from worldwide ports by the UN Security Council over suspicions that it had transported goods banned under the sanctions measures. The Lighthouse Winmore was seized upon re-entering Yeosu on November 24, foreign ministry officials told CNN.
The announcement is the second of its kind this week, further highlighting the of use of ship-to-ship cargo transfers banned by United Nations resolutions. But South Korean officials did not confirm if the Lighthouse Winmore was one of the vessels pictured.
The seizure follows that of the Lighthouse Winmore, another oil tanker which Seoul claims supplied fuel products to North Korea in October, in breach of UN Resolution 2375. He could not clarify whether they belonged to mainland China or Hong Kong.
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.
The Lighthouse Winmore was one of 10 ships the United States asked the United Nations to ban from global ports this month over its alleged dealings with North Korea, according to Reuters.
CNN's Taehoon Lee reported from in Seoul, Lauren Said-Moorhouse wrote from London while Yuli Yang and James Griffiths contributed from Hong Kong.
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