There’s the Baluch ethnic group that lives in parts of Iran and Pakistan, and they are in effect autonomous. The fake state of Pakistan tries to flex muscle there from time to time and generally fails. The Iranian mullahcracy is Shia, and the Baluch are Sunni. From the map I’d guess that’s the really dry expanse that killed a chunk of Alexander the Great’s army with thirst on their way back from India.
today:
Iran's population is majority Shiite but Sunni minorities live predominantly in the areas near the border with Afghanistan. The Sunnis have long complained about discrimination by Iranian authorities. Due to dilapidated infrastructure and a lack of health and educational facilities, the areas near the Afghan border are the poorest and least developed in Iran.
“The Taliban's leadership structures are multilayered, complicated and opaque. That makes negotiations with them difficult, and not just for Iran.”
https://www.dw.com/en/why-iran-fears-chaos-in-afghanistan/a-59630081