The top US general overseeing operations in Afghanistan said on Wednesday it is possible that Russia has been delivering weapons to the Taliban.
General Joseph Votel, head of US Central Command, told a congressional hearing that the Russians were "attempting to be an influential third party here in Afghanistan."
"I think that it's fair to assume they may be providing some kind of support to them in terms of weapons or other things that may be there," he said.
The Kremlin had organized talks last month over the situation in Afghanistan without western participation and has invited the US to join a similar conference on April 14 at which the Taliban is not expected to take part.
The security situation in Afghanistan has deteriorated with the Taliban becoming a greater threat following the withdrawal of most international troops in 2014.