A confidential US report sent to a UN sanctions committee estimated that at least 759,793 barrels of oil products had been delivered to North Korea between January 1 and May 30, well above the annual quota set at 500,000 barrels.

The illegal supplies were provided through ship-to-ship transfers at sea using North Korean tankers that have called in port at least 89 times "likely to deliver" the shipments, according to the report.

The United States requested in a letter that the UN sanctions committee declare that North Korea had violated the UN-approved quota and "order an immediate halt to all transfers of refined petroleum products" to North Korea.

The committee was expected to take five days to consider the request, which China and Russia are expected to block.

The US move at the United Nations came just days after Secretary of State Mike Pompeo traveled to Pyongyang to press for concrete steps by Kim Jong Un's regime to scrap its nuclear program.

While Pompeo said those talks were making progress, North Korea angrily accused Washington of making "gangster-like" demands for quick denuclearization of the Korean peninsula.

Pompeo insisted that a raft of tough economic sanctions imposed on North Korea would remain in place until "final, fully verified denuclearization" occurs.

Under the latest sanctions resolution adopted in December, crude oil supplies to North Korea were capped at four million barrels per year and a ceiling of 500,000 barrels of refined oil products per year was set.

But UN experts monitoring the sanctions have reported that North Korea was circumventing sanctions with the illegal imports of oil products that are vital for the country's ballistic missile and nuclear programs.

The declassified US intelligence sent to the UN sanctions committee estimated that ship-to-ship transfers may have provided North Korea with as much as 1,367,628 barrels of refined products.

In its report, the United States pointed the finger at China and Russia for continuing to sell refined petroleum products to North Korea.

"These sales and any other transfer must immediately stop since the United States believes the DPRK has breached the ... refined petroleum products quota for 2018," it said.