By Choi Ha-young

Five vessels that are being investigated by the United Nations for being involved in illegal oil trade with North Korean ships in international waters were found to be owned by Chinese businessmen, according to media reports, Thursday.

China denies its involvement in oil trafficking to North Korea, but the latest report suggests that it could have been providing oil in secret in violation of international sanctions.

On Dec. 29, South Korean authorities seized a Hong Kong-flagged vessel, Lighthouse Winmore, for an illicit ship-to-ship oil transfer in international waters.

Media reports have cast doubt on the vessel's nationality, apparently tied to Pyongyang or its allies. Last month, the United States called on the U.N. Security Council to blacklist six ships which it suspects have been transferring oil to the North. The U.S. effort, however, drew China's opposition to sanctions against five of them.

The Chosun Ilbo claimed the owners of the five ships ― Orient Shenyu under the flag of Panama; Yu Yuan under the flag of Togo; Shinsung High under the flag of Belize, Kai Xiang under the flag of Sierra Leone and Lighthouse Winmore ― are all Chinese ships, after analyzing their annual business reports.

The report claims the first three named ships are registered in Hong Kong, and the owners of the companies are all Chinese nationals. The latter two, Kai Xiang and Lighthouse Winmore, are registered in China and the companies' legal representatives are also Chinese.

Operating under flags of third countries is an easy way to evade sanctions. The Kai Xiang used to sail under the flag of Panama before operating under that of Sierra Leone. The Yu Yuan, currently under the flag of Togo, formerly sailed under the Cambodian flag. The Yu Yuan was spotted by American intelligence after exporting North Korean coal to Russia in August last year.

Only two days after the Lighthouse Winmore was seized, South Korean authorities captured the Panama-flagged oil tanker Koti transferring oil to a North Korean ship. Seoul's intelligence and maritime officials are questioning the crew, mostly from China and Myanmar.

U.S. President Donald Trump said that China was "caught red handed" on Twitter, Dec. 28. "(It is) very disappointed that China is allowing oil to go into North Korea. There will not be a friendly solution to the North Korea problem if this continues to happen."

Washington has repeatedly urged Beijing to cut off oil supplies to Pyongyang as a measure to squeeze the reclusive state, but it has refused to do so.

The Chinese government has denied the vessels were involved. Hua Chunying, a spokeswoman for the Chinese foreign ministry, was quoted as saying Dec. 29 that Beijing was "completely and strictly" complying with the sanctions.

Other than China, Russia is allegedly supporting the North as well by providing fuel oil to North Korean ships at sea in violation of international sanctions, Reuters reported Dec. 30, citing senior Western European security sources.