The newspaper Chosun Ilbo reported this week Chinese-owned vessels flying the flags of Panama, Belize and other countries were suspected of improperly trading with North Korea.
Employees at the office of Lighthouse Ship Management, the ship's registered manager, in the Chinese port city of Guangzhou, declined to comment and said they had no knowledge of the situation.
Exports of crude oil will not exceed four million barrels (525,000 tonnes) during any 12-month period, and exports of refined oil products will cease when the total approaches a ceiling of 500,000 barrels.
"It's unclear how much oil the ship had transferred to North Korea for how long and on how many occasions, but it clearly showed North Korea is engaged in evading the sanctions", the official told Reuters. The statement doesn't specify whether the ship was the one seized or among those spotted by satellites.
Prosecutors in Kaohsiung allege that a Taiwanese fishing company executive, Chen Shih-hsien, "had knowingly used ships to sell petroleum products on the high seas and had falsely written Hong Kong as the destination on the export declaration".
South Korea said Friday it had seized a Hong Kong-flagged ship suspected of transferring oil to North Korea in defiance of the sanctions.
"China has always implemented UN Security Council resolutions pertaining to North Korea in their entirety and fulfils its global obligations".
The measures follow increased Security Council penalties imposed following the North's ballistic missile test on November 29.
Democratic Progressive Party (DPP) presidential candidate Tsai Ing-wen waves to supporters during a rally in Taipei, Taiwan, Jan. 15, 2016, the day before the Taiwanese election.
In the Times interview, Trump explicitly tied his administration's trade policy with China to its perceived co-operation in resolving the North Korea nuclear crisis.
The revelations came as China denied claims by President Donald Trump it had allowed oil shipments to the North.
China a staunch communist ally of North Korea has been repeatedly urged by the global community to abide by the sanctions imposed on North Korea.
Also today, the Chinese commerce ministry said that it would reduce exports of crude oil, refined oil products, steel, and other metals to North Korea, effective January 6, in line with the stricter sanctions that the United Nations Security Council passed in a resolution at the end of December.
In November, China, one of North Korea's top trading partners, exported no oil products to the isolated country, apparently going above and beyond the United Nations restrictions.