State flags of Russia and North Korea fly in a street near a railway station during the visit of North Korea’s leader Kim Jong Un to Vladivostok, Russia, in April 2019. (Photo: Reuters)

White House national security spokesman John Kirby said, "We remain concerned that North Korea will provide further support to Russia's military operations against Ukraine."

Kirby's comments came after the United States imposed sanctions on a Slovakian man for trying to arrange the sale of more than two dozen types of North Korean weapons and munitions to Russia to help Moscow replace military equipment lost in its conflict with Ukraine.

Any arms deal between North Korea and Russia would violate a series of UN Security Council resolutions, he said. Kirby also noted North Korea's recent statements that they will not provide or sell arms to Russia.