Official Chinese customs data shows the country stuck to that pledge until August, when it imported 1.64 million tons of coal, worth about $138 million, from its smaller neighbor.
While backing United Nations sanctions, China, North Korea's main trading partner, opposes unilateral USA measures and has been anxious Washington might move to freeze its banks out of the global financial system unless they cut all ties to Pyongyang.
They reached the conclusion after investigating cyber-attacks on dozens of email accounts of employees at four local bitcoin exchanges, the Yonhap news agency said.
China's diesel exports to North Korea were 170 tonnes, compared with zero tonnes in August last year and gasoline shipments were 180 tonnes, down 96.3 percent from a year ago.
South Korea is one of the world's busiest trading hubs for cryptocurrencies, with Seoul-based Bithumb ranking as the world's largest exchange for the ethereum virtual currency.
The list is an update of a conventional arms dual-use list which the sanctions panel presented to the Security Council in December pertinent to Resolution 2321, adopted in November against the North's fifth nuclear test in September.
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Anthony Ruggiero, a senior fellow at the Foundation for Defense of Democracies, said the development "shows that China is not a reliable partner".
But Tong Zhao, a fellow at the Carnegie-Tsinghua Center for Global Policy in Beijing, said China didn't violate any United Nations sanctions with the August coal imports.
China-US ties have been strained by Trump's criticism of China's trade practices and by demands that Beijing do more on North Korea.
At the United Nations on Monday, North Korean Foreign Minister Ri Yong Ho accused Trump of declaring war on North Korea and threatened that Pyongyang would shoot down USA warplanes flying near the peninsula.
China's Foreign Ministry said on Tuesday that it will refer the question of North Korea's coal imports data for August to the customs office.