In an interview to the BBC, General Nicholson said he had seen "destabilising activity" by the Russians and weapons were smuggled by Moscow across the Tajik border to the Taliban.
However, citing lack of evidence, Russia has denied such US allegations in the past.
"We see a narrative that's being used that grossly exaggerates the number of Islamic State group fighters here," General Nicholson said.
"This narrative then is used as a justification for the Russians to legitimise the actions of Taliban and provide some degree of support to the Taliban," he was quoted as saying by the BBC on Friday.
"We've had stories written by the Taliban that have appeared in the media about financial support provided by the enemy. 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 continued.
"We know that the Russians are involved."
He also claimed that Russia conducted a series of exercises on the Afghan border with Tajikistan. "These are counter terrorism exercises, but we've seen the Russian patterns before: they bring in large amounts of equipment and then they leave."
Russia, meanwhile, denies providing weapons or funds to the Taliban but has admitted that it has had talks with the militant group. It justified that on the basis of the shared opposition to the Islamic State group, which has been trying to establish a base in the north-east of Afghanistan.
(This story has not been edited by Social News XYZ staff and is auto-generated from a syndicated feed.)
