White House National Security Council spokesman John Kirby said this week that US intelligence had concluded the Wagner Group had obtained the equipment to help its forces as they fight alongside Russian troops in Ukraine.
“We assess that the amount of material delivered to Wagner will not change battlefield dynamics in Ukraine,” Mr Kirby said.
“But we’re certainly concerned that North Korea is planning to deliver more military equipment.”
The Wagner Group rejected the claim as “gossip and speculation”.
“Everyone knows that North Korea has not been supplying any weapons to Russia for a long time. And no such efforts have even been made,” Reuters quoted Wagner owner Yevgeny Prigozhin as saying in a statement.
Neither Mr Kirkby or Mr Prigozhin offered any specific evidence to support their remarks. The military action in Ukraine have been accompanied by an attendant information war, involving various parties.
Ten months after Russian forces invaded Ukraine, increased attention has been paid to the role of private mercenaries such as the Wager Group, in the way US-based organisations, such as Blackwater, received scrutiny during the so-called war on terror.
Blackwater, founded in 1996 by former Navy SEAL Erik Prince, has been called Academi since 2011.
In 2007, Blackwater received widespread notoriety for the Nisour Square massacre in Baghdad, when a group of its employees killed 17 Iraqi civilians. While several of the fighters were convicted in the US, they were later pardoned by Donald Trump.
The Wagner Group, also founded by former military officers, has also been accused of various misdeeds and atrocities, allegations it has routinely denied.
Earlier this month, Mr Kirby claimed the Wagner Group had 50,000 fighters in Ukraine, including 10,000 contractors and 40,000 convicts.
US officials briefing the media claimed that with the alleged arms sales to the private military group, North Korea was violating UN sanctions that ban Pyongyang from importing or exporting weapons.
Ambassador Linda Thomas-Greenfield, the US envoy to the United Nations, called it “despicable” that Russia, a permanent veto-wielding member of the UN Security Council, which imposed the sanctions, was now using weapons procured from North Korea and Iran “to pursue its war of aggression against Ukraine”.
The British government also condemned Russia for Wagner alleged arm’s purchase.
“The fact that President Putin is turning to North Korea for help is a sign of Russia’s desperation and isolation,” said Foreign Secretary James Cleverly. “We will work with our partners to ensure that North Korea pays a high price for supporting Russia’s illegal war in Ukraine.”
North Korea has sought to strengthen relations with Russia as much of Europe and the West has pulled away from Moscow.