Iran fired missiles on Sunday into eastern Syria, aiming at the bases of militant groups it holds responsible for attacks in Tehran which left 18 dead last week, Iran's Tasnim news agency reported.
IRGC forces have been assisting in the fight against ISIS in both Iraq and Syria, but the missile strike represents a significant escalation in Iran's involvement.
It did not immediately offer other specifics, other than to say the missiles were launched from Iran. The Guard's website said it launched surface-to-surface medium-range missiles targeting the area.
The Guard warned ISIL militants and their "regional and worldwide supporters" that similar retaliatory attacks would target them as well if another assault in Iran occurred.
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.
The attack last week, which included shootings and at least one suicide bombing, was on Iran's parliament and the shrine of Ayatollah Ruhollah Khomeini, the founder of the Islamic Republic. Deir el-Zour is home to both Islamic State militants and civilians.
Shiite-majority Iran and Sunni-majority Saudi Arabia have long had a sectarian feud. It was the first time that ISIS, a Sunni Muslim group fighting Iranian-backed militias in Syria, has claimed responsibility for an attack in Iran.
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