This announcement is a joke. Assad is very far from Raqqah and he does not have the logistic and military capabilities to launch a ground attack against that city.
It is well-known that the troops fighting for Assad around Aleppo are mostly non-Syrian. If Assad does not have enough Syrian troops to fight in Aleppo, how is he going to open another front in the further and less important Raqqah? Will Iran send additional troops to fight in Raqqah?
What about Russia? Will Russia support an Iranian offensive against Raqqah while the Kurds and local tribes are fighting to liberate the city? How can such an act be justified?
Assad announced last week a military operation to take Dayr Az-Zor from the IS, and he even asked the inhabitants of that city to leave it (he was imitating the SDF operation in Raqqah). After that drama by Assad the IS launched an attack against the spot which he holds in Dayr Az-Zor and took a part of it. The next day there were deadly terrorist attacks in the coastal region against Assad’s Alawite supporters. After that we stopped hearing anything about Assad’s phony operation in Dayr Az-Zor, but now we hear about a new operation towards Raqqah that is even less realistic than the one we heard about last week in Dayr Az-Zor.
Assad is a clown. His military operations and announcements have been nothing but psychological games. He has sacrificed tens of thousands of his supporters in mere psychological games.
He is frightened of the idea that Raqqah could be liberated from the IS, so he is trying to foil that. The news of an Iranian advance on Raqqah will make everybody there support the IS for the fear of Iran and Assad. By propagating such news Assad hopes to strengthen the hold of the IS on the city.
Assad does not want to see a moderate government formed in Syria. He understands that if such a government is formed, many of his supporters will defect to that government. Assad prefers that the IS remains because that will continue to make him the sole option available for his supporters.