The missiles were fired from western Iran across the border into Deir Ezzor province, in northeastern Syria, targeting what the Guard called "terror bases".
The Guard said, in a statement published on its Sepahnews website, that the missiles were "in retaliation" for the June 7 attacks on Tehran claimed by IS.
"Medium-range missiles were fired from the (western) provinces of Kermanshah and Kurdestan, and a large number of terrorists were killed and weapons destroyed," the statement said.
It said the attack targeted "a command base.... of the terrorists in Deir Ezzor", Syria's oil-rich eastern province.
On June 7, gunmen and suicide bombers attacked the parliament complex and the shrine of revolutionary leader Ayatollah Ruhollah Khomeini in Tehran, killing 17 people.
The Islamic State group claimed responsibility.
Senior Iranian officials had also put the blame on Riyadh after the Tehran attacks, saying Saudi Arabia was "promoting terrorist groups" in Iran.
The Islamic republic of Iran is a key ally of the Syrian regime of President Bashar al-Assad, alongside Russia and the Iran-backed Hezbollah movement of Lebanon.
Iran has sent to Syria military advisers as well as thousands of "volunteer" fighters recruited among its own nationals as well as the Shiite communities in neighbouring Afghanistan and Pakistan since Syria's conflict broke out in March 2011.
According to a report published in March, some 2,100 combatants sent by Iran have died in Syria and Iraq.
(This story has not been edited by NDTV staff and is auto-generated from a syndicated feed.)
Get the latest election news, live updates and election schedule for Lok Sabha Elections 2019 on ndtv.com/elections. Like us on Facebook or follow us on Twitter and Instagram for updates from each of the 543 parliamentary seats for the 2019 Indian general elections.