South Korea's customs service concluded that the Lighthouse Winmore had loaded about 12,700 tonnes of Japanese refined petroleum products in South Korea on October 11, reportedly bound for Taiwan, the official said.
"China has always implemented UN Security Council resolutions pertaining to North Korea in their entirety and fulfils its worldwide obligations". The new round of sanctions has intensified the economic sanctions regime, slashing the communist state's refined petroleum product imports and banning all remaining major exports.
Beijing, which accounts for most of the North's trade and energy supplies, was Pyongyang's diplomatic protector for decades but has supported the latest United Nations measures.
China handles about 90% of the North's foreign trade.
On Thursday, Mr Trump tweeted he was "very disappointed" with China, which he said had been "caught red-handed".
"We welcome the recent positive turn of events in the peninsular situation", a spokesman for the Chinese Foreign Ministry said of the North-South Korea talks on Friday, adding hopes that "all relevant parties" will take the opportunity to bring the North Korean missile crisis "back to the correct track of peaceful settlement through dialogue and consultation". Oil restrictions have always been seen as the ultimate leverage Beijing possesses over Pyongyang, a leverage China has been reluctant to use despite frequent American requests to do so.
Ship tracking data in Thomson Reuters Eikon showed that the Lighthouse Winmore has mainly been doing supply runs between China and Taiwan since August.
The Kaohsiung-based company had leased a freighter for the cargo, and the freighter is believed to have sent oil to vessels bound for North Korea, the statement said.
There has been increasing suspicion in Washington that Chinese ships have been secretly transferring petroleum to North Korean vessels at sea.
The Trump administration has led a drive to step up global sanctions on North Korea in response to its efforts to develop nuclear-tipped missiles capable of hitting the United States.
The country's Commerce Ministry said it would impose a cap on oil supplies to the North and ban imports of its steel and other goods.
China's ministry of commerce banned steel and other metal exports to North Korea and limited exports of crude oil and refined oil products.
The UN Security Council unanimously adopted the new sanction resolution on the North on December 22nd, following Pyongyang's ballistic missile launch in November.
This defies a UN Security Council resolution imposed on 11 September.