At least 40 people were martyred or injured in a terrorist attack on a military parade in Iran's southwestern city of Ahvaz on Saturday, the Mehr news agency reported.
"There are a number of non-military victims, including women and children who had come to watch the parade", the agency quoted an unnamed official source as saying.
The "Al-Ahwaz" separatist group has claimed responsibility for the attack. Ahvaz is in the centre of Khuzestan province, where there have been sporadic protests by the Arab minority in mainly Shia Iran.
Among those involved are members of the Revolutionary Guard, a paramilitary force answerable only to Supreme Leader Ayatollah Ali Khamenei.
The deadly shooting targeted the city of Ahvaz in Khuzestan, a province bordering Iraq that has a large ethnic Arab community and has seen separatist violence in the past which Iran has blamed on its regional rivals. Some media reports said that there were four assailants and that at least two had been killed. In it, paramedics could be seen helping someone in military fatigues laying on the ground. Iran's Irna news agency says that 10 people were killed and over 20 injured. Other armed security personnel shouted at each other in front of what appeared to be a viewing stand for the parade.
The Islamic Revolution Guards Corps (IRGC) spokesman Ramezan Sharif said the attackers were affiliated to a terrorist group supported by Saudi Arabia. However, those groups in the past previously have only attacked unguarded oil pipelines at night.
However, Iran faced a bloody assault previous year from the Islamic State group and Arab separatists in the region have attacked oil pipelines there in the past.
The armed forces staged parades in several cities, including the capital, Tehran, to mark the anniversary of the Iran-Iraq war.
The assault shocked Tehran, which largely has avoided militant attacks in the decades after the tumult surrounding the Islamic Revolution.