North Korea says it hasn't exported any weapons to Russia during the war in Ukraine and has no plans to do so.
It also said US intelligence reports of weapons transfers were an attempt to tarnish North Korea's image.
In comments to state media on Thursday, an unidentified North Korean defence official told the US to stop making "reckless remarks" and to "keep its mouth shut".
Biden administration officials earlier this month confirmed a declassified US intelligence assessment that Russia was in the process of purchasing arms from North Korea, including millions of artillery shells and rockets.
North Korean arms exports to Russia would violate United Nations resolutions banning the country from importing or exporting weapons.
The North Korean official stressed that Pyongyang has never recognised the "unlawful" UN Security Council sanctions against the country "cooked up by the US and its vassal forces".
The official said the export and import of military equipment is a "lawful right peculiar to a sovereign state," according to an English translation of the statement provided by North Korea.
"But we take this opportunity to make clear one thing. We have never exported weapons or ammunition to Russia before and we will not plan to export them," said the official, who was described as a vice director general of the Defence Ministry's general equipment bureau.
"It is not sure from where the rumour originated which the US is spreading, but it is aimed at tarnishing the DPRK's image," the official said, referring to the country's formal name, the Democratic People's Republic of Korea.
North Korea has sought to tighten relations with Russia over its aggression in Ukraine, blaming the US for the crisis and decrying the West's "hegemonic policy" as justifying military action by Russia in Ukraine to protect itself.
The North Korean government has also hinted its interest in sending construction workers to help rebuild pro-Russia breakaway regions in the country's east.
In July, North Korea became the only nation aside from Russia and Syria to recognise the independence of the territories, Donetsk and Luhansk.