Story highlights Iran attack comes as region faces worst crisis since Iraq's invasion of Kuwait in 1991

Attack challenges Saudi narrative Iran is behind all regional terrorist violence

Simon Mabon is a lecturer in international relations of the Middle East at Lancaster University. The views expressed here are solely his.

(CNN) The specter of terrorism has loomed large over the Arab Gulf states for some years, but the attack in Iran Wednesday, claimed by ISIS, suggests that the Islamic Republic is now a target.

Attackers stormed the Iranian Parliament and the mausoleum of Grand Ayatollah Ruhollah Khomeini Tuesday, killing at least 12 in attacks on two hugely symbolic sites of both the revolution and the Islamic Republic.

The Persian Gulf has long endured threats from a number of Islamist terrorist groups, which have attacked a range of targets including the Grand Mosque in Mecca, Shia mosques across the region, and the Khobar Towers complex in Khobar, but Tuesday's attack is a first for Iran.

For Al Qaeda, the enemy was the West and other Muslims could help in this struggle. In contrast, for ISIS, Shia Muslims are a legitimate target and the growth in sectarian violence in Iraq has only served to fuel these differences.

For many rank and file ISIS members, the rafida -- the derogatory name for the Shia -- should have been struck in Iran much earlier, but it was the elders of the jihadi movement who urged leaders to focus upon different targets.