Curtis Scaparrotti, the top US general in Europe, said on Thursday that he had witnessed Russia's influence grow in many regions, including in Afghanistan.
In a statement to the Senate Armed Services Committee, Scaparrotti, who is NATO's Supreme Allied Commander, said Moscow was "perhaps" supplying the Taliban in fighting against US and NATO forces in Afghanistan.
His comments were rejected by Russia's foreign ministry, which called the charge an attempt by Washington to try to cover up for the failure of its own policies in Afghanistan.
"These claims are absolutely false," Zamir Kabulov, head of the Russian foreign ministry's department responsible for Afghanistan and the Kremlin's special envoy in the country, told RIA Novosti state news agency on Friday.
"These fabrications are designed, as we have repeatedly underlined, to justify the failure of the US military and politicians in the Afghan campaign. There is no other explanation."
In February, General John Nicholson, the US commander of NATO forces in Afghanistan, testified that Russia is encouraging the Taliban and providing them with diplomatic cover in a bid to undermine US influence and defeat NATO - but he did not address whether Russia is supplying the group.
Kabulov in 2015 said that Russia was exchanging information with the Taliban and saw shared interest with them when it comes to fighting the Islamic State of Iraq and the Levant (ISIL, also known as ISIS) armed group.
Russia considers the Taliban a "terrorist" group and it is banned in the country, along with ISIL.
Taliban officials have told Reuters news agency the group has had significant contacts with Moscow since at least 2007, but added Russian involvement did not extend beyond "moral and political support".
NATO troops have been fighting in Afghanistan since a US-led invasion in late 2001, following the September 11 attacks.
About 13,000 NATO service members are in Afghanistan - the bulk of them American - under its Resolute Support training mission. More than 1,800 US troops have been killed in fighting since the war began.
The US supplied Afghan mujahideen fighters with hi-tech weapons as they battled the Soviet Red Army in the 1980s.
After more than 15 years of war, US generals say the Afghanistan conflict is stuck in a stalemate with the Taliban continuing to carry broad regional influence, and NATO-backed Afghan security forces struggling to make progress.
Source: Al Jazeera and news agencies