North Korea says it has never sold weapons to Russia and has no plans to do so, following US reports that Moscow was turning to Pyongyang to replenish stockpiles.
US officials had said Russia was in the process of purchasing rockets and artillery shells from North Korea.
They said such moves, along with alleged purchases of Iranian weapons, showed Western sanctions were impeding Russia's efforts in the Ukraine war.
Moscow denied the reports at the time.
Any arms movement between the two countries would be in violation of United Nations sanctions.
On Thursday, in a statement carried by North Korean state media KCNA, an unnamed official at North Korea's defence ministry said: "We have never exported weapons or ammunition to Russia before and we will not plan to export them."
It accused the US, and other "hostile forces", of spreading rumours to "pursue its base political and military aims".
In early September, a US state department spokesman said Russia's North Korean purchases "could include literally millions of rounds, rockets and artillery shells."
But National Security Council spokesman John Kirby later appeared to caveat that statement, by saying the purchases had not yet been completed and there was no evidence to suggest the weapons would be used in the Ukraine war.
Many of North Korea's Russian-designed weapons hail from the Soviet era, but it has missiles similar to Russian ones.
The statements followed reports citing US officials that the first shipments of Iranian-made drones had been delivered to Russia, and that Russian drone operators had travelled to Iran to receive training. Iran has denied delivering weapons.
Russia's invasion of Ukraine in February has proven costly for its military, despite using advanced weapons such as cruise missiles. Ukrainian forces, using Western weapons that have been funnelled into the country in recent months, have inflicted heavy losses.
Russian-North Korean relations declined after the Soviet Union's collapse in 1991, but have gradually picked up in recent years as Russia's relations with the West have soured.
With the outbreak of war in Ukraine, Kim Jong-un's regime has blamed the US for the conflict and accused the West of pursuing a "hegemonic policy" that justified Russia's use of force.
In July, North Korea was one of the few countries that officially recognised two Russian-backed separatist regions in eastern Ukraine. In retaliation, Ukraine cut off all diplomatic ties with Pyongyang.
Earlier this month, Russian president Vladimir Putin vowed to expand their "comprehensive and constructive bilateral relations" in a letter to his counterpart Kim Jong-un. North Korea has also said it will deepen its "comradely friendship" with Moscow.