North Korea sharply stepped up trade in coal and oil products last year in defiance of UN sanctions through the apparent help of China’s shipping industry, a UN panel has said.

The annual report to the UN Security Council by sanctions experts went online on Friday and inexplicably disappeared later in the day, with the text itself noting China’s reservations about the findings.

Publishing photographs, shipping logs and submissions from member-states, the panel said that North Korea had violated the total UN prohibition on exporting coal, as well as restrictions on imports of refined petroleum.

“The continued violation by the Democratic People’s Republic of Korea of commodity export bans not only flouts security council resolutions but serves to fund a revenue stream that has historically contributed to the country’s prohibited nuclear and ballistic missile programs,” the report said.

The panel, quoting data from an unspecified country, estimated that North Korea exported 3.7m tons of coal between January and August last year, grossing around $370m.

Most coal exports were transferred from North Korean ships to Chinese barges, which often sailed up the Yangtze River to make deliveries, it said.

In a new development, North Korea has also been spotted sending coal into the ocean for pick-up on self-propelled barges that are easier to evade detection, the report said.

As North Korea’s fleet is not known to include such barges, they are likely from China, with 47 shipments from May to August last year directly reaching ports on China’s Hangzhou Bay near the economic powerhouse of Shanghai, it said.

The report said that the North also far exceeded a UN restriction on importing more than 500,000 barrels a year in refined petroleum.

Citing the United States as its source, the panel said North Korea had imported more than 3.89m barrels of refined petroleum products between January and October 2019.

China is North Korea’s primary political and economic ally and had backed UN sanctions out of frustration with Pyongyang’s nuclear and missile tests.

But Beijing has since called for an easing of sanctions after leader Kim Jong-un froze long-range missile and nuclear test launches following three meetings with US President Donald Trump.

More recently North Korea has fired a series of short-range missiles off its east coast, which the South decried as “inappropriate” amid the global coronavirus pandemic.

The United States has insisted on maintaining sanctions as leverage, although Trump has voiced admiration for Kim and recently sent him a letter with a plan to revive ties, according to the two countries.

The UN panel in February released a summary of its conclusions, but the more exhaustive report was delayed.

The full report said that China as well as Russia had asked the panel for “more conclusive evidence” of its findings.