"The prototype of very intensive negotiations on Syria underway at the moment and comprising 19 countries was largely conceived during the P5+1 talks with Iran," Vladimir Voronkov told reporters.
He recalled that Iran was not included in the negotiation process at the first stage, similar to the current status of the Syrian government.
"Restoring trust was a gradual process. Step by step, I think, if there is positive progress in the framework of the 19 countries, at some stage Syria will join," Voronkov added.
On July 14, Iran and the P5+1 group of negotiators, comprising China, France, Russia, United Kingdom, United States plus Germany, signed a historic accord to guarantee the peaceful nature of Tehran's nuclear activities in exchange for sanctions relief.
Since the beginning of the war, the United States and some of its allies and strategic partners, including Saudi Arabia, have supported the Syrian opposition and called for Assad's resignation.
In the latest round of Syria talks in Vienna last month, the international negotiators agreed that the authorities in the Arab republic and its opposition groups should kick start a political process to form a national unity government, and hold elections within 18 months under a new Constitution.
