The attackers were Iranians, recruited inside the country by the Islamic State (IS) group. They came from "certain regions," according to an official statement. That shifts the focus to the minority Sunnis, who make up 8-10 percent of Iran's overall population and are most strongly represented in regions near the borders with Iraq, Turkmenistan and Pakistan.

Iran's central government has always cast suspicion on Sunnis' loyalty - a suspicion that is apparent in the country's security policies. It is no coincidence that the president's current special adviser for minority affairs, Ali Younesi, is the former head of Iran's intelligence services.

Sunnis have long bemoaned their political exclusion in Iran: an absence of development in the border regions, the hindrance of the constitutionally guaranteed right to education in languages other than Persian and the violent measures taken by security authorities to quell peaceful protest, for a few examples. Despite all this, Iran's Sunnis have had little sympathy for terror movements.

Conflicts come home

Iran's participation in the wars in Iraq and Syria could put Sunnis' loyalty to the test. The Shiite militias that Iran is supporting in those conflicts are not only brutally attacking terror groups composed of Sunnis: They are attacking Sunni civilians accused of ties to such groups.

IS seems to be hoping to sow hatred toward Iran's central government among Sunnis. Over the past several months, the group has greatly increased the amount of Persian-language propaganda that it produces. In March, a video appeared calling for Iranian Sunnis rise up in open rebellion.

That propaganda has not gone unheard: In August, the intelligence minister announced that 1,500 young Iranians had attempted to join IS but that they had been hindered from doing so by authorities. Officials say they have uncovered 58 terror cells with connections to IS.

There has been no lack of efforts to hit Iran. The fact that IS had been unable to do so on Iranian soil until Wednesday says a lot for the omnipresence of the intelligence services and their exuberant surveillance.

Wednesday's attacks were an enormous embarrassment for Iran's security services, especially as the targets - the parliament and the mausoleum of Ayatollah Ruhollah Khomeini - were highly symbolic. Authorities will thus be tempted to further increase surveillance and their already robust presence in regions of the country where the Sunni population is highest. But President Hasan Rouhani will do all he can to keep that from happening. He received unusually strong support from voters in predominantly Sunni regions in his recent re-election.   

The course of further action will now depend on what kind of background information comes to light about the attackers. Reactions will be especially harsh should it turn out that Saudi Arabia's intelligence services were in any way connected. Iran and its rival across the Persian Gulf are sworn enemies and continue to fight for regional dominance. Still, even Iran's Revolutionary Guard will be cognizant of the fact that further alienation of the country's Sunni population could set in motion a deadly chain reaction - one from which only IS would benefit. 

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