BEIRUT—Iran is sending commanders from its elite Iranian Revolutionary Guard Corps and hundreds of foot soldiers to Syria, according to current and former members of the corps.

The personnel moves come on top of what these people say are Tehran's stepped-up efforts to aid the military of Syrian President Bashar al-Assad with cash and arms. That would indicate that regional capitals are being drawn deeper into Syria's conflict—and undergird a growing perception among Mr. Assad's opponents that the regime's military is increasingly...