The Guard's website, as well as semi-official news agencies, reported the strikes Sunday on Deir el-Zour, Syria.
Sunday's assault marked an extremely rare direct attack from the Islamic Republic amid its support for embattled Syrian president Bashar Assad. Iran's Revolutionary Guard, a hard-line paramilitary force, has seen advisers and fighters killed in the conflict.
It did not immediately offer other specifics, other than to say the missiles were launched from Iran.
The launch of surface-to-surface medium range missiles into Syria's Deir Ezzor province comes as ISIL militants fleeing a US-led coalition onslaught increasingly try to fortify their positions there. "The spilling of any pure blood will not go unanswered".
It came hours after supreme leader Ayatollah Ali Khamenei, in a statement on his website, vowed Iran would "slap its enemies" in honour of the victims' families, including those killed in Syria and Iraq.
The Islamic State group claimed responsibility.
Shiite-majority Iran and Sunni-majority Saudi Arabia have long had a sectarian feud.
"The IRGC warns the Takfiri terrorists and their regional and trans-regional supporters that they would be engulfed by its revolutionary wrath and flames of the fire of its revenge in case they repeat any such devilish and dirty move in future", the IRGC added.