In this photo provided by the Iranian Students' News Agency, Revolutionary Guard members carry a wounded comrade after a shooting during a parade in Ahvaz, Iran, on September 22.
"The number of martyrs of the terrorist incident reached 24, some of whom were women and children among the spectators", IRNA said, adding the death toll could rise further as numerous wounded were in critical condition.
State TV reports that the gunmen were on motorcycles and sprayed automatic gunfire into a crowd of dignitaries sitting on a raised platform watching the parade.
State television said the assault, which wounded more than 53 people, targeted a stand where Iranian officials were gathered to watch an annual event marking the start of the Islamic Republic's 1980-88 war with Iraq. Two of them were killed and two others were detained.
Foreign Minister Javad Zarif tweeted that "terrorists recruited, trained, armed and paid by foreign regime have attack Ahvaz".
Before we cheer too hard that Iran got hit, it should be noted that past attacks in Iran have forced crackdowns on all dissidents, not just Arabs.
Iran will be scrambling to determine the motives for the Saturday's high-profile attack as it faces growing USA pressure.
The assault by alleged militants marks one of the deadliest attacks in Iran in years and threatened to raise tensions in a region already plagued by turmoil.
Hezbollah and Iran have been at war with ISIS in Syria and Iraq for more than three years.
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Yacoub Hor al-Tostari, a spokesman for the Arab Struggle Movement to Liberate Ahvaz, later told The Associated Press that members of an umbrella group of Ahvazi activists his organization leads carried out the attack.
A statement on the Amaq news agency, which is used by IS as a mouthpiece, claimed the group was behind the attack, though this has not been verified.
However neither group provided evidence to show they were involved.
Women and children died in the assault, state news IRNA agency reported.
Ahvaz, in southwestern Khuzestan province, is home to the small Arab minority in Iran, which is mainly ethnic Persian, and has been the site of sporadic unrest.
State television blamed "takfiri elements", a reference to Sunni Muslim militants, for the attack.
In response to a question whether terrorists are affiliated with a particular anti-revolutionary group, he said "these terrorists are neither from ISIL terrorist group nor are they affiliated with anti-revolutionary ones; they have been trained in two Persian Gulf littoral states, with the help of U.S. and Mossad, and enter the Islamic Republic".
Zarif did not specify which regional government he held responsible for the shooting, but Iran s elite Revolutionary Guards said the attackers were funded by Sunni arch-rival Saudi Arabia.