Two young men were killed and two people wounded in a drive-by shooting attack at an event marking the Shia religious event of Ashoura in Iran, the official IRNA news agency reported.
Assailants in a car with no number plates approached a crowd of Shia worshippers in the city of Dezful, in the southwestern province of Khuzestan, and opened fire at around 10:30pm on Friday, the semi-official Fars news agency said, citing a witness.
Hossein Karimi Yeganeh, 28, and Bahman Rezaie, 25, were killed in the attack, and two wounded people were taken to hospital, Fars said. No group has claimed responsibility for the attack.
"It's not still clear whether the attack was a terrorist one," provincial police official Colonel Rahman Mousavi said.
"Investigators are reviewing the matter and will announce the results as soon as possible," Mousavi added.
The shooting took place at an event commemorating Ashoura - which climaxes on October 24 - marking the killing of Imam Hussein, the grandson of the Prophet Muhammad by the army of Caliph Yazid in 680 AD. That event lies at the heart of Islam's divide into Shia and Sunni sects.
A similar attack took place at a Shia site in Saudi Arabia on Friday night, where a gunman killed five worshippers before being killed by the police.
The Islamic State of Iraq and the Levant (ISIL) group claimed responsibility for that attack.