"The continuation of the DPRK's nuclear programme is a clear violation of relevant UN Security Council resolutions and is deeply regrettable," the International Atomic Energy Agency (IAEA) said in its report to members, referring to North Korea's official name.

Among activities during the period since its last report in August 2019, the IAEA said there were "indications consistent with the production of enriched uranium" at the reported Yongbyon nuclear site.

The Vienna-based agency noted in its report, dated Tuesday but publicised on Wednesday, that it had not had access to the Yongbyon site or other locations in North Korea, basing its analysis on "information available to it", including open source information and satellite imagery.

It said because of the apparent absence of steam or cooling water discharge at Yongbyon, "it is almost certain that the reactor has remained shut down since early December 2018".

But there have been indications of ongoing reactor maintenance, including the regular presence of a probable carbon dioxide tanker, as well as of other related activities, it added.

The US government, which claims that Pyongyang has pulled back on its nuclear ambitions, warned on Tuesday that the country continues to acquire materials and equipment for its ballistic missile program.

In a joint advisory the Treasury, Commerce and State departments detailed North Korea's efforts to obtain everything from forestry trucks for missile launchers to common metals and materials that can be used in rockets, warning sellers to beware of sanctions on the country.

The advisory came as negotiations between the two countries aimed at halting North Korea's nuclear weapons progress, launched with fanfare at a 2018 summit between President Donald Trump and Kim Jong Un, have remained at a standstill since early last year.

Nevertheless, two months before a presidential election, Trump and his campaign have claimed success in dealing with North Korea with Secretary of State Mike Pompeo applauding the president for "lowering the temperature".

IAEA members will gather later this month for their annual General Conference and regular board of governors meeting, which will consider the report.

In its report, the IAEA called on North Korea to "comply fully" with its international obligations and "cooperate promptly" with the agency.

In 2009, Pyongyang expelled IAEA inspectors from its Yongbyon nuclear site and has since refused to allow agency inspections on its territory.