© Atta Kenare / AFP 1434 Iranian men beat their chest during the Ashura commemorations.
The incident happened in the city of Dezful in the south-western province of Khuzestan, where a group of believers were commemorating Ashura festival. A car approached the groups and opened fire at around 22:30 local time (19:00 GMT), the Fars news agency reported, citing an eyewitness.
Ashura is a 10-day festival of mourning for the Shiite leader Hussein, who was killed by his Sunni rival in the 7th century, shortly after the schism in Islam.
A similar attack took place in Saudi Arabia on Friday, where a gunman killed five Shiite worshipers before being shot dead by police. The Sunni terrorist group Islamic State (IS, formerly ISIS/ISIL) claimed responsibility.
No group immediately owned up to carrying out the attack in Iran. Tehran is a major ally of the Syrian government, which is fighting various terrorist and rebel groups, including IS.
Comment: An ISIS attack in Turkey, a plot foiled in Russia, another attack in Saudi Arabia, and now Iran. Given that Western powers are not at all pleased that Russia has directly countered their plans to destabilize the Middle East, expect more such attacks as terror is used to send a message to anyone the West perceives as being even slightly out of step with their agenda.