At least eight members of Iran's elite military have been killed with 20 people wounded in a gun attack during a parade in the southwestern city of Ahvaz, local media have said.
Two gunmen on a motorcycle wearing khaki uniforms carried out the assault according to Iranian news agency Fars, which is close to the military.
A report on Saturday described the assailants as "Takifiri gunmen," a term used previously to describe the Islamic State group.
State press added that those injured included a woman and a child.
In footage shown on Iranian television, paramedics could be seen helping a person in military uniform lying on the ground at Ahvaz's Quds, or Jerusalem, Boulevard.
Other armed security personnel shouted to one and other in front of what appeared to be a viewing stand for the parade.
Bloodied troops could be seen in combat fatigues, helping each other walk away in images from Iranian news service ISNA.
There was no immediate claim of responsibility.
Ahvaz is the capital of Iran's oil-rich Khuzestan province, which has seen attacks on oil pipelines by Arab separatists.