The Islamic Revolutionary Guards Corps (IRGC), Iran’s paramilitary group, launched a series of ballistic missiles at Islamic State targets in Syria on Sunday in an apparent retaliation for the ISIS’s earlier attack on the Iranian capital.

IRGC forces fired the medium-range, ground-to-ground ballistic missiles from bases in the western Iranian provinces of Kermanshah and Kurdistan,according to Iranian state media outlet Tasnim news. The IRGC, which is primarily responsible for overseas military operations, promised to retaliate against ISIS for its attacks in Tehran on June 7.

“To that end the Islamic Revolution Guards Corps … a while ago has conducted missile attacks on Takfiri terrorists’ command centers, gatherings, logistic sites and factories of suicide car bombs in Deir ez-Zor region, east of Syria,” said the IRGC in a statement.

It is unclear how many missiles were fired, although a video recording uploaded to the internet allegedly shows one of the missiles passing through the night sky.

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. Previous actions centered on supporting Shiite militias in Iraq and sending troops in support of Syrian President Bashar al-Assad, a key Iranian ally.

Iran has a large and diverse missile stockpile, but Sunday’s strike is the first time it has openly used such weapons against ISIS.