• They said such moves, along with alleged purchases of Iranian weapons, showed Western sanctions were impeding Russia's efforts in the Ukraine war.
• Any arms movement between the two countries would be in violation of United Nations sanctions.
North Korea says it has never sold weapons to Russia and has no plans to do so in the future, following US reports that Moscow was turning to Pyongyang to replenish stockpiles.
US officials said earlier that Russia could purchase 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.
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.
Many of North Korea's Russian-designed weapons hail from the Soviet era, but it has missiles similar to Russian ones.
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.