Iran is made of many different ethnicities, and there were reports of Arab militants that were brought in by the regime (it’s not hard to imagine given how reliant those organizations are on Iran for support).

It’s generally not very hard to incite violence across groups in the Middle East, especially when you consider how bad the outcome might be for the losing side. Case in point, the Alawites who lost control of Syria and are now persecuted by the new government.