Denial comes after the US accused North Korea of supplying rockets and missiles to the Russian military company, the Wagner Group.

A senior North Korean official, in a statement on Sunday, slammed the US allegations as a “groundless rumour” aimed at justifying Washington’s own military aid to Ukraine.

The US had designated Wagner as a “transnational criminal organisation” earlier this month, citing the private military group’s alleged weapons dealings with North Korea – something that is prohibited by United Nations Security Council resolutions.

The White House also showed what it said were US intelligence photographs of Russian rail cars entering North Korea, picking up a load of infantry rockets and missiles, and returning to Russia.

But the director general of the North Korean Department of US Affairs, Kwon Jong Gun, rejected the accusations on Sunday, warning that the US will face a “really undesirable result” if it persists in spreading the “self-made rumour”.

“Trying to tarnish the image of [North Korea] by fabricating a non-existent thing is a grave provocation that can never be allowed and that cannot but trigger its reaction,” Kwon Jong Gun said.

He added that the US move was “a foolish attempt to justify its offer of weapons to Ukraine”.

Earlier this week, US President Joe Biden promised 31 Abrams tanks, one of the US army’s most powerful and sophisticated weapons, to help Kyiv fight off Moscow’s invasion.

The move drew a rebuke Friday from Kim Yo Jong, the powerful sister of North Korean leader Kim Jong Un, who accused Washington of “further crossing the red line” by sending the tanks into Ukraine.

Kwon Jong Gun reiterated Pyongyang’s concerns over the tank transfer on Sunday, calling it an “unethical crime” aimed at perpetuating an unstable international situation.

Along with China, Russia is one of North Korea’s few international friends.

Russia, one of the five permanent members of the UN Security Council, has long held the line against increasing pressure on nuclear-armed North Korea, even asking for relief from international sanctions for humanitarian reasons.

Meanwhile, other than Syria and Russia, North Korea is the only country to recognise the independence of Luhansk and Donetsk, two Russian-backed separatist regions in eastern Ukraine.

In November, after the White House said Pyongyang was covertly supplying Russia with a “significant” number of artillery shells, North Korea said it had never had arms dealings with Russia and had no plans to do so.