In an interview with the BBC last week, General John Nicholson said that Russia had been acting to undermine U.S. efforts in Afghanistan despite shared interests in fighting terrorism and narcotics, with indications that Moscow was providing financial support and even arms, themoscowtimes.com reported.
"We've had weapons brought to this headquarters and given to us by Afghan leaders and said this was given by the Russians to the Taliban," he said.
A statement from the Russian Embassy in Kabul dismissed the comments as "idle gossip," repeating previous denials by Russian officials.
"Once again, we insist that such statements are absolutely baseless and appeal to officials not to talk nonsense," the embassy said.
U.S. commanders, including Nicholson, have said on several occasions over the past year that Russia may be supplying arms to the Taliban although no confirmed evidence has so far been made public.
However, Nicholson's comments were unusually blunt and came in a context of growing tensions between NATO members and Moscow over the case of Sergei Skripal, a former intelligence agent found poisoned with a rare nerve agent in Britain.
Russian officials have said that their limited contacts with the Taliban were aimed at encouraging peace talks and ensuring the safety of Russian citizens. Moscow has offered to help coordinate peace talks in Afghanistan.
Taliban officials have told Reuters that the group has had significant contacts with Moscow since at least 2007, adding that Russian involvement did not extend beyond "moral and political support".
Moscow has been critical of the United States and NATO over their handling of the war in Afghanistan, but Russia initially helped provide helicopters for the Afghan military and agreed to a supply route for coalition materials through Russia.
Most of that cooperation has fallen apart as relations between Russia and the West deteriorated in recent years over the conflicts in Ukraine and Syria.