North Korea maintained and developed its nuclear and ballistic missile programs throughout 2020 in violation of international sanctions, according to a UN diplomat citing a confidential report.
The report by independent sanctions monitors said Pyongyang "produced fissile material, maintained nuclear facilities and upgraded its ballistic missile infrastructure".
It also continued to seek material and technology for the programs from abroad.
The annual report to the UN Security Council's North Korea sanctions committee comes just weeks after US President Joe Biden took office.
A State Department representative said on Monday the administration planned a new approach to North Korea including a review with allies "on ongoing pressure options and the potential for any future diplomacy".
North Korean leader Kim Jong Un and former US president Donald Trump met three times in 2018 and 2019, but failed to make progress on US calls for Pyongyang to give up its nuclear weapons and North Korea's demands for an end to sanctions.
In the past year, North Korea displayed new short-range, medium-range, submarine-launched and intercontinental ballistic missile systems at military parades, the UN report said according to the diplomat.
While there were no nuclear or ballistic missile tests, Pyongyang "announced preparation for testing and production of new ballistic missile war heads and development of tactical nuclear weapons".
North Korea's UN mission in New York did not immediately respond to requests for comment.
North Korea has been subjected to UN sanctions since 2006.
They have been strengthened by the 15-member Security Council over the years in a bid to cut off funding for Pyongyang's nuclear and ballistic missile programs.
In 2019, UN sanctions monitors reported North Korea made at least $US370 million ($A482 million) by exporting coal, which is banned under UN sanctions.
But last year, they said coal shipments appeared to have been largely suspended since July 2020.
The isolated Asian nation imposed a strict lockdown last year amid the coronavirus pandemic that has slashed its trade, hurting an economy already burdened by international sanctions.
More than 40 countries accused North Korea in July, however, of illicitly breaching a UN cap on refined petroleum imports.
The UN sanctions monitors said imagery and data provided to them by a unidentified member state showed Pyongyang had breached the annual cap of 500,000 barrels "by several times".