The Free Syrian Army has rejected offers of military support from the Russian government, stating that they could not be trusted.
A spokesperson for the western-backed rebel alliance told the BBC that Moscow's help was not needed.
"[Russian President] Vladimir Putin, is assisting a regime that indiscriminately kills their own people," Issam al-Reis said.
"How could we trust the Russians' help?"
Mr Issam told the BBC the FSA would continue fighting President Bashar al-Assad, who "was not part of the solution" to ending the conflict.
"If the Syrians stood with Assad he would not ask for invaders to come to Syria," he said.
Russia's Foreign Minister Sergei Lavrov said Russia was prepared to give the rebels military support if they attacked Islamic State militants. Mr Lavrov also asked the US to share information about rebel positions.