The sophisticated ISIS attack in Tehran is a major operational success for the group. This is an early attempt to analyze the event based only on Iranian official sources.
After two years of efforts, first to penetrate the well-guarded Iranian border with Iraq, then build an infrastructure in the Sunni provinces of Ahwaz (or Arabistan), Kurdistan and Baluchistan from where to reach the capital Tehran, ISIS finally succeeded to strike at the heart of the Islamic Republic’s symbols, during the holy month of Ramadan: Ayatollah Khomeini’s mausoleum and the Parliament, and probably a third target of civil infrastructure.
It is of note that on March 26, 2017, ISIS published a 37-minute video accusing Iranian Shi'ites of committing many crimes against Sunnis and oppressing the Sunni population of Iran, "exporting the revolution," spreading Shi'ism, and secretly collaborating with the US and Israel. The video ends with a statement: "We tell you, oh Zoroastrian Rafidites: Our hands are not far from you. Just as you tasted our power in Iraq and Syria, thus, Allah willing, we will conquer Persia and restore it as a Sunni country."
Last year Iranian authorities foiled a plot by Sunni militants to bomb targets in Tehran and other cities during the Muslim holy month of Ramadan.
For the background on this period, see this author’s article “ISIS and the Sunni Separatists Aim Fire at Iran,” published on June 7 at https://www.ict.org.il/Article/2022/isis-and-the-sunni-separatists-aim-fire-at-iran