Bloodied troops could be seen in combat fatigues, helping each other walk away in images from Iranian news service ISNA.
Iranian armed forces members and civilians take shelter in a shooting during a military parade. Ahvaz is in the centre of Khuzestan province, which has been the site of sporadic protests by Iran's Arab minority.
The parade was marking the start of the Iran-Iraq War, which lasted between 1980 and 1988.
Two of the attackers were gunned down during clashes with the security forces and two others arrested, one of them injured, IRNA said. At first, those present appear to think that the gunfire could be part of the ceremony, but then quickly realize it is a hostile attack and immediately begin to scramble from the scene.
Iran : At Least 12 Martyred, 30 Wounded in Terrorist Attack (VIDEO)
"Individuals disguised in the Islamic Revolution Guards Corps and Basij uniforms fired at officials and people from behind the stand, leaving a number of innocent people including women and children martyred or injured", Governor of Khuzestan Province Gholamreza Shariati said.
Iran's Tasnim news agency, citing a local official, reported that at least 10 people had been killed, including a journalist.
Meanwhile, Guard spokesman Gen. Ramazan Sharif told ISNA that an Arab separatist group carried out the attack, without elaborating.
Saturday's attack comes after a coordinated June 7, 2017 Islamic State group assault on parliament and the shrine of Ayatollah Ruhollah Khomeini in Tehran. At least 18 people were killed and more than 50 wounded in the attacks. The assault shocked Tehran, which has seen few militant attacks in the decades after the tumult surrounding the Islamic Revolution.
Najib Razak held over $628m linked to 1MDB, to be charged
However, U.S. authorities have said Tanore was controlled by an associate of Low and held funds diverted from 1MDB. The former leader was questioned by police and then appeared in court in the capital, Kuala Lumpur , on Thursday.