Ali Maqsoud in an interview with FNA said that Iran and Russia's continued aid and military support for Damascus means that formation of a US-planned government by the ISIL is no more possible.
Iranian President Hassan Rouhani and his Russian counterpart, Vladimir Putin, plan to meet in Russia's city of Ufa next week, a Kremlin spokesman said.
Russian President Vladimir Putin meets Iran's new president for the first time this week, reportedly armed with an offer to supply missile systems and build a second nuclear power reactor that is likely to trouble the United States.
Saudi Arabia has attempted to entice Russia through a package of economic incentives if Moscow agrees to scale back its support for the Syrian government.
Russian President Vladimir Putin has held a rare and previously unannounced meeting with Saudi intelligence chief Prince Bandar Bin Sultan to discuss the situation in the Middle East.
Moscow has stressed National Security Agency (NSA) Whistleblower Edward Snowden will not be extradited to the US.